I'm running the latest 5.5.10 kernel in Fedora 31 and the Parallels module are (finally) working fine.
To get Parallel Tools to compile properly (when I was running 5.5.8), I made the two changes in prl_fs and prl_vid and, for some reason, had to recreate some symbolic links in /lib/modules/ as they were pointing to old versions:
cd /lib/modules/5.5.8-200.fc31.x86_64/weak-updates/
rm prl*
ln -s /lib/modules/5.5.8-200.fc31.x86_64/extra/prl_eth.ko.xz
ln -s /lib/modules/5.5.8-200.fc31.x86_64/extra/prl_fs_freeze.ko.xz
ln -s /lib/modules/5.5.8-200.fc31.x86_64/extra/prl_fs.ko.xz
ln -s /lib/modules/5.5.8-200.fc31.x86_64/extra/prl_tg.ko.xz
ln -s /lib/modules/5.5.8-200.fc31.x86_64/extra/prl_vid.ko.xz
Since then, I've had two kernel updates (5.5.9 and 5.5.10) and everything is working fine.