@KintsugiUwU With the RC2 release I have also started updating the Flatpak build, see Prepare update to Picard 3 by phw · Pull Request #302 · flathub/org.musicbrainz.Picard · GitHub .
The test build there is available for installation via:
flatpak install --user https://dl.flathub.org/build-repo/319104/org.musicbrainz.Picard.flatpakref