Psycho-Werefox
There is already s suggestion above. Here you can find (in general topics) some official solutions from GOG staff
https://support.gog.com/hc/en-us?
But ofc you shouldnt restrict yourself with only GOG support site. Ms one, Square Enix Eu.
I can give another suggestion. Trivial one exist for 30 years - close every other applications. I guess both black screen and input problems are come from one source - some Input decive plugged + tools for them. GOG support site refer to LogiOptions.exe that it have silent overlay (that make even appearance glitches, not only input).
Kill that process (i hope everyone here can use task manager properly).
GOG staff refer to this in specific article for specific game:
https://support.gog.com/hc/en-us/articles/360019811033-Diablo-missing-menu-text?product=gog but as i say - it is trivial solution work for 30 years. It should be mentioned also somewhere in general solution.
Just replug input or other usb devices and kill (uninstall entirely) that applications. They not needed and NOT GAMINS tools.
Also headsets can cause problems. Or sometimes fix. Nowadays headsets is for smartphones that use one plug for speakers and micro. Nowadays 3'5 audio jack be same - one for both sound input and output.
And still better... usually better - to use USB headset made only for using on PC. or very simple headphones.
Check sound settings also. Keep an eye on differences when you plug even audi-jack phones - current Windows can recognise even simpelst phones as differ audio device. Ofc USB is differ as well (that phones have audio chip build-in).
Check output quality, exclusive mode and else settings when you plug and unplug any headsets.
Same for every MSI\etc tools. And even GeForce Experience. This is not needed and harmful software for gaming PC systems. Ofc especially for old games. If you cant just configure game settings - you better switch to console gaming.
...........
Also, GOG put own GOG DX DirectDraw wrapper (old wrapper actually, but updated in silence with differ games\catalogue updates; some wrapper builds are made for specific games some if general). It is came with DXCFG.EXE tool - you should go to game folder (always should) and start as - as admin of course.
GOG also put DX DirectInput wrapper (i see that for fisrt time, of course i can miss it) - but it didnt have config tool, just dixi.ini file.
I cant say what it in there - check yourself.
it it still better to use legacy DirectInput devices for old natively Dinput games even if game prepacked or you download some wrappers.
................
What the matter pointing to reviews that they about game itself and not GOG release?
EVERY... E-V-E-R-Y games on Steam and GOG have threads where everyone there complain that game DO NOT WORK AT ALL!!!111 speaking for everyone. Literally. When you faced them that at least for someone game work, they continue complain "no, it is broken release!!!" and "broken, refunded, wait for update from GOG" reviews.
They also blame soft for Microsoft broken hands and stupidity. It is OK when Microsoft staff or volunteer mods on community.microsoft.com say that every apps devs should make them soft compatible with every "security updates" that no one needed and not a security at all (real security hotfixes do not broke any applications or backward compatibility).
But we here shouldnt speak in that way. Every updates builds of Win10 - is like differ OS with so many broken things each time. Most of them made even for purpose.
We cant expect any tweaks on devs\publishers\GOG side to make our PCs work properly. If some app didnt work - by default it is PC(hard\soft) didnt handle it. We should find why. Very rare it is because of game itself... and that not for such old games. It even made not for WindowsNT OS. Back in Win9x there some requirements-specification for fullscreen 3d-application (some of them are stupid ones even back then) that never be compatible with NT OS (again, because of Ms stupidity - initially NT is not for home PCs and not for gaming). And that old games work nowadays sometimes because devs back then DONT follow that specifications.