Welcome to 
This portal contains links to the various Debian wiki pages regarding graphics cards and their respective driver installation processes. Almost all graphics cards have free and open-source drivers available in Debian, however some cards may have better compatibility and performance after installing proprietary firmware or proprietary drivers.
If you don't know your graphic card, visit hardware identification page to identify it, then find more information on its setup by matching it to one of the pages below.
If you get a fixed low resolution (like 1024 x 768) with no choice of higher resolution in GUI and/or xorg-server log errors with missing device (like (EE) open /dev/dri/Card0 no such file or device) and/or non starting display manager (sddm etc), make sure that your kernel is up to date (as the kernel has to recognize the graphics device). Also make sure that the appropriate firmware packages are up to date.
Technical words can be used but explained.
AMD/ATI
Intel
If your graphic card was manufactured in 2007 or later, try uninstalling the xserver-xorg-video-intel package and use the builtin modesetting driver (xserver-xorg-core) instead.
For older devices: xserver-xorg-video-intel
nVidia and nouveau
#nouveau, official channel
Optimus at Nouveau wiki (this link is the recent X documentation )
Mali
MaliGraphics - General page with details on Mali GPUs, information on how to install the proprietary drivers
PanfrostLima - Information on the free and open-source Lima and Panfrost drivers for Mali GPUs
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