Thank you all for your input!

@rolfie and @kapqa:

I need only 2D framebuffer stuff (most challenging is youtube 4k). I now am thinking whether I should use that old GT730 or that K2000 lying around, just to evaluate how Nouveau has improved meantime. No need for a 300 watt turbofan engine

@grunchy:
great to see that other Devuan users also are big ZFS fans
Actually I used ZFS on root on Debian for years, until a RAM ECC error halted the system very roughly and destroyed the data pool (the last snapshot was still readable, though). After that I switched back to FreeBSD. But, as said, FreeBSD is less than ideal for desktop usage, no hibernate support and other things.

@zapper:
I guess I just should try again Nvidia/Nouveau after that long time...

But what worries me a bit right now is that I need to help debug some KDE packages and have to build/install them manually using custom options. I read that is extremely difficult on Debian/Devuan in comparison to FreeBSD or, say, Void Linux. Iiuc in the former, one has to modify the build scripts themselves, while in the latter one can concentrate on the options setting, without fear of trashing the whole system. But maybe that is just dramatized? *scratching head* Whatever, this makes me ask what is more advisable, devuan or void... please excuse me, I am still trying to understand before I start the project...

Thank you all again