HDMI hot plug not working any more in bullseye

["Harald" <debian-bug@lobo.uber.space>]

Hi,

if just updated to bullseye and now, HDMI hot plug does not work any more.
I have a GeForce GTX 960 (AMD64 system) with a monitor connected through a DVI-D cable and a projector connected through a HDMI cable.
If I have the projector switched on at system startup, everything is fine, but if the projector is switch off at startup, I have no way to add it as display when switching it on afterwards.

With Debian Buster, this worked.

Using KDE, nvidia-driver.
Tried system settings of KDE and nvidia-settings. Both worked with Buster.

Any ideas how to get hot plug back to work or where to find additional hints?

Thanks,
Harald