For quantity, ITunes, though situation is the same as Qobuz - Win/Mac only (plus no FLAC files). Also Ototoy though mainly for the Japanese market and some stuff here and there are geo-blocked (but at least downloads work on browsers).
For game OSTs, Steam (needs to download through their launcher but has the most options), GOG (requires base game) and Itchio (has the least among the three).
For more niche stuff, Bandcamp, but also is the best for browser downloads.
Though small, apparently ITunes and Recochoku, and confirmed by me the artist Nigel Stanford's store, all sell music videos too, but on ITunes yet to confirm DRM status as I've seen conflicting and scarce information, Recochoku is geo-blocked in its entirety, and purchases on Nigel Stanford's store are annoying to make and then to manage and download (plus exclusive to his works).
I have some others noted down but they're too small and without relevant aspects I can think of to mention.
@mpanhans I use Bandcamp but you won't find much mainstream music. On the other hand, you won't find much mainstream music.
@vkc