X1 (4th gen) does not boot anymore from USB, can't upgrade

Hi

I am running Ubuntu 16.04 on my X1 (so I successfully installed it). I
just generated (using unetbootin) a bootable USB stick with Ubuntu
20.04 and tried to boot my X1 with it. 

It did not work, he just passed directly to the already installed 16.04.
So I tried the old USB with 16.04 and it did not work out neither.

I attach a photo of my BIOS setting, I am deeply puzzled. 


Any help would be really appreciated.

Regards

Uwe Brauer