Not sure why “direct profit” is important.
Proton is basic infrastructure for Steam Deck (which runs Linux). Valve has sold millions of units that I doubt would have been sold without Proton. There’s just a ton of games that will never be ported to native Linux.
Proton isn’t only Valve’s doing though. It’s heavily built on top of Wine which is a very mature open source project that has seen extensive leadership and contributions by CodeWeavers.