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.
Robert McBroom