What was the purpose of you writting as the very first sentence of your post:
Steam doesn’t enforce the use of its DRM (which is super easy to bypass anyway but that’s a side note).
If not to tell us that Steam also sells DRM-free games?
If Steam also sells DRM-free games (even if alongside games with DRM) then de facto Steam is a seller of DRM-free games.
Being a "seller of" doesn't mean just selling that and nothing else.