[solve] Slade 3 - suddenly green flickering lines everywhere

[P1NKAC1D]

I was just using Slade 3 as usual, adding some graphics, editing some decorate stuff, when out of nothing a strange graphical bug appeared. The whole preview/editing window has an overlay of green, flickering lines like this:
https://s12.directupload.net/images/201005/roermm2w.jpg

I closed it and started again, still there. Restarted the computer, no success, still green flickering madness. Checked graphics card drivers - they are up to date., Re-installed Slade 3, tried different versions, it's still the same. I have absolutely no idea why this happened and how to get rid of it. It seems to be something specific to Slade, because I tried other applications (Ultimate Doom Builder, some games etc.) and nowhere else this error appeared.

Did I accidently activate a "special mode" or something by pressing a certain button? Or what may happened here? I couldn't find ANYTHING like this by searching on google or in forums... And it's not usable in this form :/

[P1NKAC1D]

I have been helped at the official Slade Discord server. Just in case anybody else encounters similar problems, this link helped:
viewtopic.php?p=1165738#p1165738

In my case, I installed new drivers for the Intel UHD graphics card (checked only the drivers for my Nvidia card before...)
Certain onboard graphics cards seem to have problem with OpenGL or something and cause stuff like this