Interesting. Looking at the second image: When you click "Insectoids", then the current entry is replaced by "Insectoids"?
I could produce the image myself, but when I click "Insectoids" nothing happens, nothing gets changed.
How are you running Stars!? I can play Stars! via DOSBox (Windows) or otvdm, and I tried my (legal) full version and a downloaded shareware version, always the same behaviour. The rest of the game works fine, including custom race generation and custom game creation, except that I can't edit the second page of the custom game generation process? Clicking the blue diamond works, only the very last step fails - I can't change any entry.
Any idea?

Like I said: I'm using Wine.

I gave up on Windows some time in 2016.

I feel like I last heard of OTVDM some years ago.

Forget using DOSBox. I just tried it (for the 1st time) with DXWnd and it runs perfectly, as far as I could tell.

Thanks - you helped me solve the mystery! Although a part of the mystery still remains.
First of all, I can customise the races on my PC now, by running Stars! under DOSBox For Windows.
The remaining mystery is that this didn't work only a couple of hours ago.
There is one thing I did after I had read your post mentioning Wine. Stars! is still played today, mostly MP, for example in the Stars! Autohost environment. To do this, it MUST be possible to edit the race screen. I'm pretty sure that not all MP players use Wine. Consequently, I searched the Autohost forum more thoroughly than before, and came across a recommendation to use a special configuration of DOSBox For Windows to run Stars! - which I did. And out of a sudden I could edit the races. Then I went back to my normal configuration of DOSBox For Windows, and it worked there, too.
Finally, I launched Stars! via otvdm (a utility to run 16bit programs on 64bit PCs), and the problem was still there. This means it's a bug (or deficit) of otvdm. For my conflicting experiences in DOSBox For Windows environments I still have no explanation, but I guess I can live with that. :-)
Thanks again.

If you want to play the game, here is a distribution that has a preconfigured emulator. Stars! v2.7j - WineDVM 0.7

Considering that the game is no longer sold and Mare Crisium is dead as a doornail, I doubt we will see an official Stars!.

Oh, I thought it was a legal grey area, that's why I thought that while it is NOT legal, it isn't technically illegal either.

Thanks for clarifying.

So disregard what I said, no legal way of getting Stars! besides buying a overpriced used and barely functional ebay copy.

No, the issue is the skimmers don't see psecifically what your issue is, 'cause you confused them with dosbox, and the issue you're having in particular requires first that people run it. Since you're not really providing enough details, you're probably better off moving this discussion to an area with more specific experience to your game rather than general experience. I'm probably one of your best bets in this thread, but seeing as i don't have the game, and i can't find a safe way to get it, i can't figure out what you're doing wrong. And, your attitude isn't helpful, either.

Neat! I never had problems running Stars! on Win10, but it's always good to have an alternative.
I noticed that your package is based on otvdm. Which kills my theory that otvdm is the culprit (apologies, otvdm!), because the race setup screen works when I use the package, but not when I run Stars! with otvdm directly. Looks like there is a communication problem between otvdm and Win10, wbhich goes away when I add another software layer (WineDVM) between otvdm and Win10. Well, I'm not expert enough to understand or explain it.

I understand and appreciate what you're saying, but I disagree. My first post was describing the problem fully and adequately - for those who are familiar with Stars!. It doesn't mean anything for all other people. And this was intentional.
If you play Stars!, you know what custom game setup is, and you know that there is a window where you are supposed to be able to edit the participating races, and I said that it doesn't work for me. I could have worded the question differently, like: Are you experiencing the same problem? But honestly, I never expected this to be a general bug. There are too many people who still play Stars!, and the problem would have been mentioned on some forum (I did search the internet before posting). I chose GOG for asking my question simply because it appeared to be the simplest way for me, saving me having to register elsewhere. And I had made the experience just a few days ago that a similar question on the same GOG forum, regarding Mordor, led to an interesting discussion. Besides, Stars! is a "Good Old Game", for me at least, so to discuss it here is justified for me. If there wouldn't have been a reaction, I would have tried other means, but it wasn't necessary - my problem has been solved, I learnt something new, and I now have a new tool which may turn out to be very useful when I run into problems with other old games.

Yes, if you don't know Stars!, then you can't help. And I wasn't expecting anyone who doesn't know Stars! to even try to help. You criticise my attitude. I apologise, if I have offended you, it was not intended. But I noticed that there were several replies where I couldn't see a relationship with the topic, and (initially), too few which answered my question (sorry, but Resident Evil, and ways to obtain Stars!, and legality issues are off-topic for this thread). I don't mind off-topic posts (and your question was an understandable one), but I was afraid that my question would get lost.
I admit that I misinterpreted darvond's reply that for him Stars! runs fine under Wine initially - but we managed to clarify this issue very productively.
Regarding your question: I didn't answer it, because I wasn't sure how to do it. To discuss "abandonware" on a forum is problematic (Canuck_Cat's reply describes the issue well), and I decided not to participate myself. I'm sorry to have offended you.

"PEBCAK"! I love the term! :-)
But it's wrong. Not that I would exclude (my) human error a priori. But I tried too often, consulted the manual to find out if there is a situation where it might not work, and I repeated the same steps over and over again in different environments. Don't tell me that I forgot the controls" in one environment, and not in another. And when it eventually worked, I didn't do anything differently.
That it didn't work in DOSBox initially, but did later, is still mysterious for me. I may have made a mistake in the beginning, but why repeatedly, why only in DOSBox, and why did I avoid making that (hypothetical) mistake later? It's as likely as that my memory doesn't work - but it works well in other contexts.

Have you tried running in a virtual machine running Windows 98 to see if the issue still persists (either via Virtualbox or equivalent) or emulating a mid 90s PC (via PCem)? The issue with games like stars is that they came from a bit of a nightmare period for keeping games working on modern hardware - not DOS, but not a modern DirectX either...

Well... legality in general is a fairly binary thing. Anything that isn't illegal is legal. Grey areas just mean people haven't worked out which one something is yet - it's not a permanent status.

No, but I may, out of curiosity. As far as I'm concerned, this problem is solved: I have found two ways to run Stars! with full functionality, and I haven't been able to avoid the problem when I use a third approach. Unfortunately, the technically simplest tool (as fara as I can tell), otvdm, to run Stars! seems to have a certain problem with custom game generation (everything else works), all working tools are VMs based on an OS. VirtualBox or PCem might be other tools of this kind.

Yes, they're pretty much VMs running an older OS. Personally, for gaming, I prefer PCem as it effectively emulates an old gaming PC and is pretty customisable - and provided you don't want to use anything that needs more than a P233, it's pretty reliable. It's worth setting up if you've got other old things you want to use that doesn't work with the wrapper for Windows.

Out of interest, when you say Windows via Dosbox, is that 3.11 or are you somehow getting Win95 working that way?

The version of WineDVM (thus OTVdm) is from 2019. Unfortunately, the github page doesn't have a prebuilt release with the updates. I tried to use Cmake to create a build from the master, but my computing skill is pretty lackluster. You seem more technically inclined, and might be able to get a newer build running.