At night the worldview - but not the character portraits and etc. - goes black. This is, apparently, not a new bug and it's game-breaking (as well as annoying since you waste a lot of gametime resting for sunrise.)

I've tried fiddling with various graphical controls - in the game, and in the DirectX settings - no luck.

I've got the Intel(R) UHD Graphics driver - this is the default driver on my HP laptop.

I realize people don't generally like this game much but I have some nostalgia for it.

I guess this is the same issue as here:
https://www.gog.com/forum/might_and_magic_series/mm9_black_screen_during_nightin_water

but I can't figure out from the thread what the solution actually was, if any?

I suggest you to try installing dgVoodoo 2.

Follow these steps:
1) Download the latest version of dgVoodoo 2 from here;
2) Extract the archive into a temporary directory;
3) Enter the MS\x86 folder and copy D3D8.dll, D3DImm.dll and DDraw.dll files into the game's installation directory;
4) (OPTIONAL) Run the dgVoodooCpl tool in order to configure the settings.

Same issue: Black screen at night and in water. It apparently has to do with Intel integrated chips.

I have tried with no success:

Compatibility (no effect)
DDrawCompat, multiple versions (crashes on startup)
dgVoodoo (I can get the game to freeze, that's about it)
Replacing files with NOLF's black-screen underwater fix (a few posts claimed this worked for them, but only crashed my game)

There was apparently a fan-made fix-all patch for this and other problems but it is no longer hosted.

It's amazing that the answer to this problem is known but has become lost in the depths of the Internet...

Perhaps tried.
But Control Panel-> Program and Features> Program Compatibility Troubleshoot

And how! But alas, no results. Toyed with all compatibility options, absolutely no effect. Changed compats on main, launcher, Lithtech, etc.

The game starts up and plays fine. When you go underwater, the screen flickers and then goes black. As soon as 5pm hits, the screen goes black.

Many people have gone through the game simply avoiding those two situations. (Camping at nightfall, and nothing essential requires underwater exploration.) It just seems like I'm missing even more of what many people call an "unfinished" game to begin with.

But I do want to play through, for completionist cred, as I purchased the series and it's the only one I've yet to play.

Use the experimental version of DDrawCompat.
v0.2.1 and older versions don't have the fix for this issue.

If it crashes, check if your system supports the 800x600 resolution (e.g. try setting your desktop to that). If it doesn't support it, you might be able to add it as a custom resolution in your Intel Graphics Control Panel (at your own risk).

If the resolution is not the problem, then please download ddraw-debug.zip from the experimental release and use the ddraw.dll file from the ReleaseWithDebugLogs folder. Reproduce the issue with it, then send me the DDrawCompat-lithtech.log file for debugging. It would be best to open an issue for this on GitHub, if you can.

I left a message on Github.

The problem with DDrawCompat is that the game crashes immediately, and so I can't get to where I can reproduce the problem.

My computer has that resolution option.

I'll repeat part of the Github message here, just in case anyone else knows what the heck is going on!

Using Experimental version, Windows 10, Dell Inspiron 620 Desktop, Intel(R) Core(TM) i3-2120 CPU @ 3.30GHz, 8gig ram.

From DDrawCompat-lithtech:

3c8c 11:34:55.818 Process path: C:\Program Files (x86)\GOG Galaxy\Games\Might and Magic 9\lithtech.exe
3c8c 11:34:55.818 Environment variable __COMPAT_LAYER = "HighDpiAware"
3c8c 11:34:55.818 Loading DDrawCompat dynamically from C:\Program Files (x86)\GOG Galaxy\Games\Might and Magic 9\DDRAW.dll
3c8c 11:34:55.820 DDrawCompat loaded successfully
3c8c 11:34:55.821 Installing display mode hooks
3c8c 11:34:55.821 Installing registry hooks
3c8c 11:34:55.821 Installing Direct3D driver hooks
3c8c 11:34:55.822 Installing Win32 hooks
3c8c 11:34:55.827 Hooking user mode display driver: igdumd32.dll

This may help. Don't know and no time to search.

https://www.pcgamingwiki.com/wiki/Home

.... and later that day.
Here's the page on the wiki site for ix
https://www.pcgamingwiki.com/wiki/Might_and_Magic_IX

I'm the one who put together all the fixes a couple years ago. Sadly, since getting a new laptop, am now having issues getting the game to even start when replacing the .dll files from dgvoodoo2.There is a certain release of it that worked in the past, but GOG, sometime in the past two years, added Windows 10 compatibily, which makes the OTHER fixes obsolete, but still leaves the black screen underwater problem, and it seems to have invalidated the previous fix. This is, without question, the most immensely frustrating game to keep functional among the thousands I own.

Edit: so, it DOES still work with a certain version of dgvoodoo2. You need to download version 2.55.4.1 from March 1, 2019, take the files in the MS folder, drop them in the folder, and, assuming the game actually starts without crashing, you it should fix the problem. The only drawback at this time is you have to use the task manager to force quit the program to get rid of a small window after you close the game, which is small poatoes compared to the other problems this game has had, and probably will again. This works as of the time I am writing this. Can't promise a future Windows update won't kill it again.

As for people saying they can complete the game with the black screen problem, I mean, ok, maybe you CAN do it. But I know for a fact that the first dungeon requires an underwater section. You'd basically be blind and have to guess with your keyboard movements. One of the promotion quests takes place on a dock at night. Not sure how the hell you would complete it this way, nevermind the fact that you'd constatly have to avoid the 12 hours of every game day that has the night sky.