On Thu, 27 Aug 2020 at 19:02, Robert McBroom via users <users@lists.fedoraproject.org> wrote:
What does one do in the new environment to run different versions of
linux on different drives of a system. One system has f31 on sda and
centos7 on sdb. With legacy grub I could call the boot of one system
from the other and vice versa. No more. Switching drives in the bios no
longer works. I can kludge things by putting the boot files from the
centos7 system in the f31 boot and putting the boot stanza in the as a
custom entry in grub.d along with the stanza for Windows.  All the
entries in /boot/1oader point to the f31 system. grubenv is only
appropriate for f31.

Second system has f32 on sda and f31 on sdb.  The f32 system is the only
one that will boot. There are entries in /boot/loader for both. but only
f32 will boot.  Seems to be an issue on boot in the root versus boot in
a boot partition.

There are boot managers for UEFI, https://rodsbooks.com/refind/ is one 
example that I have used (but not with the latest incarnation of grub2).  

--
George N. White III