i finally managed to start my computer with ubuntu 20 and nvidia working (driver 455 nvidia-bug-report.log.gz (322.0 KB) after disabling secure boot) but it looks like low resolution like on the image… i attach also the bug-report…
The kernel is too old for the AMD gpu, please upgrade to the latest HWE:
https://wiki.ubuntu.com/Kernel/LTSEnablementStack
Afterwards, please create a new nvidia-bug-report.log