Would it be much work to cache the artist names and images in the Plex desktop apps so the scrolling doesn’t stutter and you don’t see black boxes? It’s jarring and makes user experience feel pretty crummy. If library size is an issue then you could paginate the requests to prevent any potential performance issues.
I’d just switch to a different client but there aren’t many to choose from in Mac OS if I want to stream music from my Plex server.
There’s an existing feature suggestion to cache artwork to improve playback (generally for all clients vs. only desktop apps).
I suggest to comment/vote in that existing thread instead of distracting/dispersing them within a duplicate thread. That is unless you strictly veto and insist on keeping this one dedicated to desktop clients alive.
As for streaming music on your Mac… have a look at Plexamp (requires a Plex Pass membership)!