Well, I have to say that Harmonoid is the best one I've found, it has a ton of cool features, it works and it allows you to be able to see your collection by album and it doesn't use Electron. Right now its development has stalled a bit but it's still pretty much in good shape, though.
I want to like Strawberry as a way to connect to Subsonic server on Linux, but it's just so clunky. I hate list view, as well as the theme..
Have you tried Sublime Music (GTK)? I used other (Electron) alternatives but Electron sucks, Sublime Music feels pretty fast.
I have and it's great but I use KDE so I prefer a QT-based player
Which theme? If you configure it right it should match the system theme. Here's what mine looks like on Plasma 5, Breeze Dark.