You could take a Look in the Program ''Disks'' and check there in the Settings of the Drives if there are set up as Automount on Start Up.
Hm. GRUB doesn't look for OSes by default. As I recall, there was some edge case security issue with os-prober (what it used to find EFI for itself and create things). If GRUB is misconfigured, that's certainly not helping, but it doesn't sound like you're in a state where you can change grub's config.
If someone here knows how to set it to probe, you might try that. I know the config line is
GRUB_DISABLE_OS_PROBER=false, but I'm not sure how to reflect that when using E to do a one-time edit of the GRUB config.