Because none of the solutions on PCgamingwiki and gog and steam forums worked for me I got playing around with dgVoodoo 2 and got good results.

Step 1: undoing compatiblility settings.

If for some reason the compatibility settings for div.exe are greyed out, the only way to undo them seems to be deleting the compatibility settings in the registry.

type "regedit" in the searchbar (windows 10, use Win+R for older windows).
Now goto:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\AppCompatFlags\Layers

and delete both Divine Divinity entries.

Now rightclick on div.exe in the gamefolder and select properties, in the compatibility tab uncheck "run this program in compatibility mode for", check "disable fullscreen optimizations", leave checked "run as administrator".
In "change high DPI-settings" uncheck everything.

Step 2: setting up dgVoodoo 2

Download dgVoodoo 2 here:
http://dege.freeweb.hu/dgVoodoo2/dgVoodoo2/

Extract (drag and drop) dgVoodoo.conf and dgVoodooCpl.exe to the gamefolder with your favorite extraction tool (I recommend 7zip).
Then goto the MS\x86 subfolder and extract all the files into the gamefolder.

Now in the gamefolder open dgVoodooCpl.exe and click on the DirectX tab.
There uncheck dgVoodoo Watermark (or leave it on if you wish) but leave everything untouched, especially DO NOT check Fast video memory access.

Step 3: setting up the game

In the gamefolder open configtool.exe and select Direct 3D, for resolution I've chosen 1280 x 720 as that keeps the text readable and the GUI remains useable, AlphaBit seems to turn itself off every time I open this tool so I leave it off and I have checked Smoothness.

Step 4: setting up the affinity mask

In order to make the game run more stable we make the game run on a single thread.
In file explorer browse to the gamefolder and in the gamefolder rightclick on a empty space and select "new" and then "text file". Let's call this file "DD.cmd" (the .cmd part is important) and copy paste the following line:

start /affinity 2 div.exe

Save and exit.

So that's it, now always start the game with DD.cmd, you can change your shortcut so it points to this file or make a new shortcut of it.
If you still want sharper graphics (e.g. because you have a 4k display), goto the dgVoodoo2Cpl.exe > DirectX tab and in resolution select 2x, 3x or 4x depending on your hardware (for a 1080p display 2x is enough), selecting 1080p directly or any of the other modes results in a worse looking picture though.

Divine Divinity should run a lot smoother now with quicker loading and save times and hopefully it also runs more stable.

Thank you! This is the best fix I ever saw! Works great!

You're welcome, glad it helped! :^)

Thank You. this makes the game playable, works perfect

Nice, thanks!

I've increased the VRAM to 512 MB in the voodoo control panel, directx tab, near the "dgvood virtual accelerated card"

I've got some crashes before like the games was struggling to keep up with the stuff on screen. occasionally there are some really short stuttering in the music not very often in some areas but no crashes anymore, all works fine.

it doesnt work

Could you elaborate?
Maybe we can find out what's the problem.

Hi! I followed the instructions but it didn't work on my PC. I have been fiddling around for hours. Updated my GPU drivers to the latest. Tried Divine Divinity from Steam, tried a different ddraw.dll. The only thing I haven't tried is experimenting with GPU settings because I don't know what to turn off first.
Attached is a screenshot of what my game looks like now. My character is just a dark shadow. Cabinets and shelves are totally dark, too.

I'm using an NVIDIA 2080 Super GPU and Windows 10.

Hmm, maybe try this, open the dgvoodoo control panel (dgvoodoocpl.exe) and select a different output api instead of the best available one.

The highest level often is the best, if it doesn't help try a lower one.

Thank you, but I already tried that. I've checked every offered directx output api.

I've tried software mode now, but funny thing is, the charakter and shelves are still dark, but all shadows are gone. Maybe someone with better technikal understandings than me has an idea now.

Problem solved! :)

In the compatibility settings I must use 16-Bit colors! Now it works. I'm happy.

Strijkbout, could you please check if you use this setting too and if so put it in your guide?

Sorry for the late response, I will check once I get the game reinstalled.
I stopped playing DD some time after I made this guide and it's on a computer I currently don't have access to.
Could it also be that that 8/16 bit color mode is a recent addition in Windows? Cause I don't remember it, then again I just could have overlooked it.

Still glad you got the game working, which is the important thing.

edit:
Okay I installed and played it on my current computer but on my side everything is fine with 8/16 bit colors unchecked.
Are you sure you have selected direct 3d in the configtool?

I'm trying to run the game on a newer build with an Intel i5 13600K CPU and GTX 1080ti GPU, and the game keeps making the CPU temps jump to about 61c despite the usage percentage only being about 7%. Any idea why this game would make the temps jump that high and how to fix it?

Maybe turn on v-sync or limit frames to 60 fps or so.