before you start commenting that TUI musicplayer xy is the best, my priorities:
must have:
support for m3u playlists (synced to Android with Syncthingy) should autodetect them in a single folder I use also for the music files, and read/write them
support for viewing all files
support for custom music directories
support for deleting music files
Flatpak OR clutterfree on KDE
would like:
Pipewire output
nice simple GUI
modern, clutterfree design OR customizability
subtitles, cover images, etc.
I used G4Music which looks awesome and has minimal playlist support. It works really well but it cant write to the playlist. It is blazingly fast, and I made an issue, offering a bounty for write-to-playlist support.
I found Lollypop, the old GTK UI is way better than the Qt alternatives, while still kinda ugly. But it seems to tick all boxes, apart from Pipewire support.
What I tried:
G4Music
UI perfect
no file deletion
no playlist addition
no playlist creation
Lollypop
UI is bareable
pulseaudio, no setting at all
playlist support including writing to! You need to enable it
lots of internet stuff for artwork and subtitles
sane defaults
GNOME music
does not detect my .m3u playlists
slow
needs pulseaudio
settings are a joke
no folder view
Strawberry
UI is horrible and not customizable enough
no Pipewire support
no .m3u detection
cluttered, no UI zoom possible
system icon theme is not applied
Clementine
like strawberry but different?
more online stuff
interface less customizable
cursor broken on the Flatpak
Amarok
Strawberry in even older?
bloat?
retro-development status
MusicPod
UI hides too much stuff
no playlist support
no filesystem hierarchy support
strange Ubuntu look, but good UI, fancy background
no podcast backup file support (so Kasts is better for that)
but pipewire support!
Plattenalbum
no playlist support
otherwise looks great
Resonance
modern, GTK4 Libadwaita, UI is damn lit
freezes, fills up the entire RAM (scans every title at once!) -> not optimized at all, made system freeze and needed to hard shutdown.
no playlist support?
no pipewire support?
Melody
uses soon EOL GNOME 42 runtime
Amberol
beautiful but too minimalist
why are there soo many GNOME music players??
moosync
very nice UI
electron: tiny cursor on Wayland, no Pipewire support
plugin support for Youtube, Spotify (using librespot) and LastFM
No it will use ALSA, Jack or often Pulseaudio. Pipewire can plug into these, but this causes overhead and to my knowledge doesnt allow things like external Equalization.
I may have to give Elisa another try. I think Strawberry (and Clementine) and Elisa suck. They are completely unintuitive, the UI has too many buttons and options for random stuff, and basic things you expect dont work.
I'm pretty sure Fooyin meets all these. It's still very early in development but I like it more than any of the other native Linux music players I've tried.
I've been down this rabbit hole as well. They all have problems but I'm most happy with Cantata for library playing (beets for file/tag management) and deadbeef for odd local files and file conversation.
The lack of a really good, customizable player on Linux has been probably my least favorite part of the whole experience. Deadbeef is close, but it seriously needs a good media library plugin.
For that reason, I'm still using foobar2000, which is Windows-only but available as a Snap using wine (and yes, I hate Snap). I check regularly to see if there are better native options, but even with the clunk from Snap and the relatively ugly UI due to wine, foobar remains superior IMHO. I think it checks all your boxes, except it's a Snap.
I dunno if VLC can do "Pipewire output", but I think it does a lot of the other stuff you mentioned. I use it on my desktop (Mint) and my phone (Android) and it suits my needs at least.
Hm, VLC is an unofficial (but very well done) Flatpak, no Wayland support and a bit bloated and not well suited for playing music afaik. But I may have to give it another try.
The new 4.0 version of VLC looks very cool, but it is only available from an Ubuntu PPA which I used with a Ubuntu Distrobox, but no way that sucks too.
Should do some Github action to extract the binary from that PPA and pack it into a Flatpak.
MPD + some GUI client. Plattenalbum is one such client but it's an outlier because its album based when MPD is playlist based.
directories for music or playlists are configurable
supports alsa, jack, pulseaudio, and pipewire
album art is up to the client
deleting music is up to the client.
Cantata is another GUI mpd client that I've used and enjoyed. It's unmaintained but would other fit your needs. I also recommend installing mpDris for mpris support.
It is for the most part as minimal as it looks, except that it's actually quite good for playlists and managing one's music collection.
It doesn't have a ton of devs behind it, so I would be surprised, if they had native Pipewire support already. Otherwise, I think, it covers what you've listed.