ubuntu 20.04.1 with nvidia GPU: not responding brightness control, not responding touchpad, black window in nvidia-settings

I have an ubuntu 20.04.1 system with a NVIDIA Quadro T2000 and an integrated Intel(R) UHD Graphics 630. After a recent ubuntu update, I have the following problems:

• I can't change the screen brightness, not with keyboard hotkeys, nor via the terminal (using xblacklight),
• the touchpad is not responding,
• the external monitor, connected via HDMI, doesn't recieve a signal anymore, and
• when opening nvidia-settings the window appeares, but it is black and emtpty.

I tried installing the nvidia drivers from a different ppa:graphics-drivers/ppa(as suggested here Low fps on games and no animations after update), but that did not change anything. Via the additional drivers I changed back to the nouveau drivers; again, no change.

The biggest issue is the maximum screen brightness which blasts my eyes away. I'm fine with only using the intel graphics card - I can switch to my windows partition if I need graphics power.

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