Just in case anyone's still stuck with the SBAT issue on the Linux systems and can't easily disable secure boot for whatever reason - boot a live Fedora image, open a terminal, run
sudo mokutil --set-sbat-policy delete
and reboot. shim should now clear the sbat policy and you're back in business. Don't allow Windows Update to run again until things are sorted.
If you need help trying to figure out what version of Node, Ruby, Postgres, Redis, Elasticsearch, Libvips, FFmpeg, ImageMagick you need to upgrade your Mastodon instance you can always check out https://www.mastoreqs.com in addition to reading through the release notes of the new version.