They basically made the game incompatible with some of the unofficial patches, more unstable and said "yup, work is done here" :D

Ok, so GOG doesn't care at all anymore? So the information about taking care of old games and people who play them is just an advertising ploy? Shame on you GOG, I really had a better opinion of you. Not only did you break something that worked, but you still don't do anything about it and ignore the gaming community. Are you taking a cue from Ubisoft? Is that really the right direction?

Sadly in the last 6 or 7 months they could just have reverted to the last correctly working version of DAO they had (the one just pre-"preservation" ) and take time to think on how to do their "preseveration" correctly for this title, but they did nothing and people that are interested to buy that game on gog will be left with this "performance crippled - DLC not showing" version.
Shame on gog indeed

The preservation did a lot of good for some games ( good old Final Liberation by example) but they really did a bad job on this DAO

That's exactly what I was thinking - let them restore the previous, fully working version.
The worst thing about GOG is the fact that they completely ignored people who paid for the Ultimate version, not the regular basic version. No one from GOG even bothered to write anything

There is a way to roll back to the previous version and use the add-ons. In GOG Galaxy, when you are in your library, click on DAO. Then press the configure button (next to the play button). Manage installation --> configure. There we select the previous version, click ok. Wait for it to update and that's it. The add-ons are in the game again.

At least I can see the DLCs under "Installed content", and the AddIns.xml (and offers.xml?) are not empty, which I understood was the reason why the DLCs were not showing. So at least that DLC part seems to have been fixed at some point.

On Windows the game still seems to be restricted to two logical CPUs, so that part is still unchanged. Then again I am unsure which is the correct fix for that because as far as I've read, for some people the game is more stable when the affinity is restricted. So if they removed that restriction, maybe the game would be more unstable for many people?

Funny thing though that if you install the game in Linux with e.g. Lutris, it appears the game runs on all cores. So in Linux that CPU affinity restriction doesn't seem to apply.

Setting the game's core affinity to use all cores fixed my slowdown issues. I just arrived in Ostagar, game would run at 40-50 fps, sometimes it dipped into the 30s. After setting the affinity through the task manager, the game runs with stable 100 fps most of the time. It seems like it really is as simple as reverting the core limit that GOG has implemented. I'm honestly kind of shocked that GOG refuses to fix the problems they have created... 9 months later. Please do something about this, this is not a good look for the preservation program.

After 50 hours filled with slowdown and performance issues, I stumbled upon this thread. Setting the game's core affinity to use all cores fixed my slowdown issues as well. The game is running beautifully now. I can't believe GOG is leaving the default version the way it is--they're usually better than this.

Kinda intrested after playing it back then on the playstation, but the steam version is just nothing but crashes, so i thought about buying it here, since gog is known to "fix" their games for modern pcs, but now i read there are a lot of problems. Did they fix the crashes yet?

I haven't encountered any crashes yet in my ~10 hours with the game and I'm using a couple of mods. The only problem this port has is the core affinity setting, you need to manually change it every time you want to play. Other than that it works without problems.
I wasn't sure if GOG already patched the game's exe to use 4GB so I just applied the 4GB LAA patch again just to be sure.

I understand correctly that there is now offline installer only the latest broken version?
is there any news about the new fix?