NewRetroWave is the GOAT.
They've posted over 3000 retrowave and synthwave songs and albums since 2011, and more keep coming. With over a million subscribers, they're one of the biggest players in the YouTube synthwave scene, and for good reason: in an era of low-effort compilations repeating the same tired tracks over and over, NewRetroWave somehow keeps finding quality fresh material for us listeners. Most of their posts are single songs (3-6 minutes), but there's a few longer (hour-ish) compilations mixed in.
This feels less like a YouTube channel and more like a library. Definitely check it out!
Going to be honest, I have no idea how this channel works. I think they go out and find music then post the best stuff they come across.