Ok! It will take a few days because I have to do much work till monday and this means that I have not the time to switch to Linux. I have checked diskpart and diskmgr in Windows. Both show the same result as lsblk. Windows is installed on nvme0n1. Part 1 is system reserved, part 2 is drive “C”, part 3 is the recovery partition.
Grub should be installed on a FAT32 partition, shouldn’t it?
I have never seen short a UUID.
At the moment both OS boot without problem. I am not able to read the grub.cfg, so I don’t see what is wrong. But I have found out that Windows boots when when I select “insmod part_msdos”.