Themken: Yes, drivers... do you have the central graphics files added as PPAs so not to have to wait for Mint team to offer them a few years later.
Seems to be fixed for now.
It seems some packages or dependencies or whatever were broken. I don't know why it didn't report errors before, but at some point I started getting some errors and also Synaptic package manager reported of 3 broken installations (somehow related to nvidia).
I tried to clean the cache and sudo apt-get install -f but it didn't work and Synaptic couldn't fix it either but after one or two reboots and changing drivers to the open source nouveua drivers, "sudo apt autoremove" removed some nvidia stuff, and after a reboot, now I finally got the hires desktop back, and screen brightness controls work too (I had some issues with them before, the brightness would always be at full when I booted to Linux and had to manually lower the brightness; now it finally works fully ie. remembers the brightness setting after a reboot).
The Driver Manager still recommends me to switch to Nvidia 390 closed-source drivers, not sure if I dare to try them anymore or just stay with nouveau drivers. Yeah I know people say NVidia's own drivers are "much better" but for some reason I never saw any real difference, even with games (= playing Team Fortress 2 on Linux). They seemed to work the same to me.
Anyways...