grub2 not detecting all operating systems when booting

I have 4 different OSs on 4 SSDs, sda thru sdd. When I run

sudo grub2-mkconfig -o /boot/grub2/grub.cfg

I get:
generating grub configuration file …
Found Ubuntu 20.04 LTS (20.04) on /dev/sda1
Found SUSE Linux Enterprise Desktop 15 SP1 on /dev/sdb1
Found SUSE Linux Enterprise Desktop 15 SP1 on /dev/sdb1
Found openSUSE Leap 15.1 on /dev/sdd3
Found openSUSE Leap 15.1 on /dev/sdd3

Note that it doesn’t list fedora-32 on sdc.
Then I run:
sudo grub2-install /dev/sda

and get
Installing for i386-pc platform.
Installation finished. No error reported.

When I boot the choices are fedora-32 or Ubuntu, but not the SUSE OSs.
How can I add the SUSE OSs as boot choices?

As mentioned in other threads, the “Found X” messages come from the os-prober script and therefore list all the other OSs present on the system.

I think that you are using a BIOS GRUB configuration on a UEFI system, so grub.cfg is actually read from /boot/efi/EFI/fedora/grub.cfg and not /boot/grub2/grub.cfg.

See this and pay attention to the differences between the two.