FLAC can be compressed while maintaining lossless quality, unlike WAV.
The point about bigger filesize is valid though. Streaming FLAC is pretty useless, as you mostly cannot hear the difference between OPUS and FLAC. Opus is used on Youtube and other platforms, free lossy codec.
FLAC really only makes sense for archiving, if you want to encode with a future lossy codec. Or if you work with music and want to do crazy things like slowing it down, or changing the pitch.
It might be that you just changed the settings in the Tidal app, or the app has a different quality preset when installed new.
Dont stream FLACs, you likely cannot hear a difference and as said, FLACs are huge. About 20 times larger than OPUS files.
Https://github.com/boredsquirrel/media-scripts