Muffon. It’s not a Spotify Client but it does play music that comes from Spotifys library along sides Deezer etc. It’s super good imo, I don’t even have a Spotify subscription anymore due to it, cuz it’s that good, thought you can only use it on PC/Laptop atm though.
I’ve been using Hyperpipe though for a while on my phone, which has a PWA, which has been working super well since BeatBump started to not work for me, alongside teething problems with using Spotube.
There was Blackhole player too but that been dead for a long while now.
Mine’s Mirlo. It’s not owned by a big corporation, plus it’s open source too, with an ability to customise your own artist page, just like bandcamp, alongside being able to help and contribute to independent artists as well.