@jonas Thanks for getting back to me!
I got Strawberry from the Arch Linux extra repo. Coincidentally, the package was updated a few minutes ago to add the missing API credentials part haha, so the part you mention about rebuilding the package (since it's done directly from git I assume) has been done.
@materpris23
The desktop file has been renamed since the previous reply, normally should be /usr/share/applications/org.strawberrymusicplayer.strawberry.desktop
Maybe there is an issue with Tidal authentication when using flatpak, try a native package.
@Devilishly_Jaded
You can't use a client ID from https://developer.tidal.com/dashboard, if that's what you've tried, that's not compatible. You need to use a client ID from a registered application that Tidal allow to get stream URL's without unencrypted.
@breversa
Tagging using inline editing in the playlist for files outside the library was broken, I've just fixed it.
If you are on linux you can try the latest from https://builds.strawberrymusicplayer.org/