Has anyone tried modding the new versions? I'm mostly interested to know if it's okay to use Tweaks Anthology and Unfinished Business on these, and to a lesser degree Ascension and BG2 fixpack.

Do you know about the gibberlings3 forums? You should be able to get more info from the mods' subforums there. Unfinished Business is not on there, I think, but you can always ask in the General thread.
https://www.gibberlings3.net/forums/forum/34-tweaks-anthology-forum/

Yeah, that's where I get the mods from, the question has been asked by someone else weeks ago but they got no answer.

testing mods takes time

No shit... I was wondering mostly about any obvious errors during installation (weidu usually lists those) since I don't have time or space (it's a spacetime thing) to experiment right now.

Since the latest version of Weidu 247, BG2 modding is nearly at a standstill. Lots of installation errors/problems. I highly suggest everyone use version 246.
Until Weidu 248 comes out I highly doubt revised versions of all of our favorite mods will come out for this new BG2EE version.
Latest weidu releases at Github:
https://github.com/WeiDUorg/weidu/releases

Just for your information:

For BG 1 EE + SoD I've tried to install mods Unfinished Business (which asks for Merger 1.3 in case of SoD) and Classic Movies. Classic Movies works (but with some issues) if installed before anything else, Unfinished Business does not for version 2.6.6 (but works for 2.5. and older) no matter what. There were unconfirmed rumors about version 2.7 coming some time in future (I guess 2.6.6 is what was meant by "coming in 2.7"), so there are no other options but to:

1) wait for anyone from modding community create the working mods
2) or install the BG EE version 2.5 or older with all the mods you like, the only problem is that in 2.6 and later Beamdog finally fixed the horrific path-finding system but there is one issue though, you characters can't push each other if someone stand in the way and it's easy to get them stuck, you might stuck in doorways and on screen transition as well, not fun. (The same issue present in vanilla BG1-2 where characters also have serious brain problems with navigation).

Links for checkup:

DLC Merger 1.3 - 4 Jan 2021
https://github.com/Argent77/A7-DlcMerger/releases
https://github.com/Argent77/A7-DlcMerger/releases/download/v1.3/win-64bit-A7-DlcMerger-v1.3.zip

Unfinished Business 16.4 - 26 May 2021
https://github.com/Pocket-Plane-Group/bg1ub/releases
https://github.com/Pocket-Plane-Group/bg1ub/releases/download/v16.4/bg1-unfinished-business-v16.4.zip

Classic Movies 2.3.1 - 4 Jun 2021
https://github.com/Sampsca/BGEE-Classic-Movies/releases
https://github.com/Sampsca/BGEE-Classic-Movies/releases/download/V2.3.1/bgee-classic-movies-v2.3.1.zip

Baldur's Gate EE 2.6.6 - 18 May 2021
https://store.steampowered.com/news/app/228280?updates=true
https://store.steampowered.com/news/app/228280?updates=true&emclan=103582791433838365&emgid=4719187892133917376

Okay, we have Weidu 249 released last November:
https://github.com/WeiDUorg/weidu/releases

What about mods? Any expectations?