I sometimes like to resize my browser window to half the screen width and noticed that GOG Forums don't really fit in that.
So I decided to fix it on my end. Found that I can change web page styles with Stylus extension and wrote my custom User Style: userstyles.world/style/22171/gog-forums-shrinker (apparently I can't add full links (yet?))

Maybe it will help someone else too.

Some limitations:
1. Just now noticed that post list still doesn't fit the narrow width (I could fix it later).
2. Posts with long links in it still break the width (Don't know how to fix that yet).

Thanks for sharing.

You can go to https://www.gog.com/forum/mysettings and select the experimental theme, which is easier to modify and works better with modern screen resolutions.

text-overflow: ellipsis; or overflow-wrap: break-word;

Tried overflow-wrap before, didn't help (as I checked a already has break-word), tried text-overflow now - also didn't help.
This only works with fixed width Ooh, nice, thanks. Then the User Style is obsolete. New theme solves the issue!

You need at least 10 forum reputation points to post links. You can check your current total on the forum settings page linked above. You get 1 point for each day that you post. If I recall correctly, you get 5 points if 5 people upvote your post to mark it "high rated" or your post is marked as the solution to a question thread.