DeGoogle Yourself

Yep, look but don't touch unless it's for personal use. Not ideal, but I think it's a step up compared to a completely closed source alternative.

I can somewhat understand the reasons, particularly looking at the fake NewPipe app malware on the Play Store, and Louis' own experiences of being screwed over by other lobbyists while trying to pass R2R legislation in the cleanest possible condition. Trademark protection + GPLv3 would have mostly sufficed I think, but an explicit "prohibition" by license allows for a much faster legal conclusion AFAIK.

The unusual license may also be to allow distribution on iOS at some point, as GPL licensed software is not allowed on the iOS app store without dual licensing (although this is not something I'm familiar with). GPL components can be embedded within apps though I think.

Grayjay is pretty much a frontend viewing and development interface for media platform plugins, and every plugin is AGPLv3 licensed. Someone could make a Purplejay or a Greenjay alternative frontend implementation for them and there'd probably be no issue.

Having fewer SA & FOSS apps that take the place of several closed source apps is great: Newpipe (or my preferred fork, Tubular) handles soundcloud, youtube, and bandcamp. Grayjay handles patreon and nebula. It also doesn't hurt to have multiple apps capable of playing YouTube in the event that they break one app with some new change, as NewPipe, LibreTube, Grayjay's plugin and yt-dlp all use different extractors AFAIK