I am running Ubuntu 20.10 (GNU/Linux 5.4.0-70-generic x86_64) on a Lenovo P70. I worked with an external monitor connected to the thunderbolt port. After the last update of the NVIDIA drivers the machine lost the external monitor. It is not listed in xrandr output and using an HDMI cable does not help. The monitor works perfectly.

How could I solve this problem?

Thank you ind advance.