There were some talks to migrating all PolyMC Flatpak installations to Prism Launcher, which was achieved by marking PolyMC as outdated on Flathub’s repo and marking Prism Launcher as the newer version, which will result in Flatpak clients replacing PolyMC with Prism Launcher while moving data over. The only thing users would notice is that the icon and name on the apps list changed, since all worlds and instances would stay in place.
Unfortunately I think they didn’t continue with this decision.