Comment 6 for bug 1940783

I tried now manually grub mk-config.
There already is the wrong menuentry "ubuntu" which in reality is Linux Mint:
    menuentry 'Ubuntu' --class ubuntu --class gnu-linux --class gnu --class os $menuentry_id_option 'gnulinux-simple-78393152-82ab-40fd-a659-eb7649202665'

os-prober doesn't even find my presently running Mint on sda5 but everything else:
/dev/sda1:Windows 10:Windows:chain
/dev/sdb1:Windows Recovery Environment:Windows1:chain
/dev/sdb2:Windows 10:Windows2:chain
/dev/sdb6:Linux Mint 20.2 Uma (20.2):LinuxMint:linux

Something is terribly gone wrong here since the last update of grub.
I don't have a clue how to fix it. Do you have any hints?

But I think this ticket can be closed since the root cause seems to be grub itself. Your grub customizer is just the place where the error becomes visible to me. :-(