If you have a "rescue" option in grub then boot it, the rescue install
should be built with hostonly=no and is expected to include all
drivers including that one. I verified on one of my machines that one
is included in my rescue. The normal initrd is hostonly=yes and only
includes the critical modules needed to boot the system, and thin was
not previously need and so not included.
Once booted rebuild the other initrd and that should include the thin
module now.
lsinitrd <initrdname> | grep -i thin should show you if it gets put
into the initrd after the rebuild and can be used to confirm that it
is not in any initramfs except rescue.
I went the dumb path.
I made a regular logical volume, used partclone to restore my back up and then booted into the OS.
Once booted in I added the following to /etc/dracut.conf:
add_drivers+=" dm-thin-pool "
and then rebuild by initramfs by
dracut -f
and then booted into my other two fedora kernels and did the same.
After that, I created the thread pool and thin volumes again and restored my backup again, and logged in.