Navidrome will do that.

The workaround I use is to connect my phone to my computer via bluetooth, and then linux/kde acts as a speaker/headphones.

So then, phone audio goes through my computer instead. I just play all audio or podcasts on my phone, and that's how I sync up my playlists, and where I'm at in them.

On Android, Vanilla Music has it. Although the app is unfortunately semi-broken on newer Android versions and not being updated anymore, because Google came up with an even more fucked up API for accessing files in the filesystem.

Deleting songs doesn't work anymore. Not sure, what else is broken...

https://f-droid.org/packages/ch.blinkenlights.android.vanilla

I use foobar2000 on android, not sure it does what you want but it does import .m3u playlists

I also like fossify music player, works with playlists but not sure about scanning like you say https://f-droid.org/packages/org.fossify.musicplayer

Ive been using opentune (from fdroid) that i use for youtube music (you have to log in to a youtube accnt, but it lets you download off youtube), this also scanned my phone for files but again not sure about playlists

i mostly just listen to albums because i am a very sophisticated person :p

I just need to play music for free.

Sigh

So annoying...