NitroPad Ubuntu boot issue: Invalide signature on kexec boot params

I updated Ubuntu and now face the same issue as discussed here. The difference is, that the proposed solution does not work for me:

Please try “Options” → “Update checksums and sign all files in /boot”

My attemt results in:

failed to update checksum ...

Who can give any advise?

Is it maybe this problem:

This works for Nitropad NV41 v2.4:

date -s 2024-03-01
hwclock -w

Thanks a lot!