I can't remember exactly what I did, but I think I copied an F31 install onto an existing F31 install on a hard drive that had Windows 10 on it.   I did this in early 2020.  Didn't keep notes. :(

Now I have a hard drive that will boot Windows 10 fine, via the Windows 10 Boot Manager.

When I go into the BIOS manager, it shows 2 boot options: Windows 10 via the Windows 10 Boot Manager and the hard drive device itself.

If I choose Windows 10, Win 10 boots fine.  :(
If I choose the hard drive device itself, the BIOS says to insert a valid boot device.

When I look at the hard drive with GParted, I see this:

Samsung SSD 850 EVO mSATA 500 GB with:
/dev/sdb1   ntfs Recovery (Windows)
/dev/sdb2  fat32  EFI System Partition Has a boot flag
/dev/sdb3  unknown type  Microsoft Reserved Partition
/dev/sdb4  ntfs  Basic data partition
/dev/sdb5  ext4    <--- this is the boot partition, has the boot stuff on it.  Has a boot flag.
/dev/sdb6  lvm2 pv   fedora

A fedora "device" which has 3 partitions:
/dev/fedora/home  ext4   the home directory
/dev/fedora/root   ext4
/dev/fedora/swap  linuxswap

I used a live USB version to facilitate the copy.  I suspect that the live boot got installed (thus the FAT32 partition) instead of the real boot partition, which is /dev/sda5 right now.

How do I fix this ?

Thanks