Do you have a hint for me how to recreate it?
I‘ve found this issue:
https://github.com/QubesOS/qubes-issues/issues/6210
Seems to be related. Will try this.
You need to boot from some live system and chroot your Qubes root
partition which properly mounted EFI partition. Then run:
'dracut -f /boot/efi/EFI/qubes/initramfs-{version}.img {version}'
Maybe a better option is just modifying xen.cfg for booting an older
kernel and then try to reinstall last kernel package after properly
freeing some space.
This way you only need to mount your EFI partition (no LUKS, no LVM,
etc....) and edit the file xen.cfg.