I listen to a stream of a Los Angeles station called KUSC all the time. It’s a fantastic station (unless they’re doing a pledge drive, but don’t worry, they just did one) and it’s comforting that it’s the same hosts no matter where I travel.

Asking to play it works across all major devices and platforms.

I used to listen to KUSC until I got annoyed with the commercials and interruptions, of which there are quite a few. Now I recommend Radio Swiss Classic (http://www.radioswissclassic.ch/), which is better in this respect; the music may be of slightly less variety and with less scommentary.

KDFC.https://www.kdfc.com/

KUSC listener here too. I agree it's great station, plus it's available on my quite old Squeezebox devices. It's owned and operated by the University of Southern California

Not exactly what you mean but operacast lists opera streaming broadcasts from around the world:

operacast.com

It's pretty old-school but I've found the schedule pretty up-to-date. I've also noticed that some of the programs aren't opera per se but "opera adjacent", like choral music or instrumental music by opera composers. My impression is that there are some programs that regularly stream operas but at any given week might offer something else.

My sense is that there's a lot of opportunity for a well-done classical streaming service. A lot of the traditional channels don't quite work because their catalogue isn't deep enough or their metadata structures are weird and unhelpful (for example, it's impossible to sort by composer alone).

Opera cast is generally pretty great, but it is pretty manual and they do miss a lot of things going on. There are now lots of classical streaming only services like Primephonic, Idagio, and others that take care of the metadata problem.

If you can access UK radio via the internet we have BBC Radio 3 and ClassicFM.