Has it really been that long? Apparently so. Valve originally announced their rebranding of Steam Play with Proton back on August 21st, 2018. Seems like a good time for a quick reflection being halfway to a decade old now with the tech that gave rise to the Steam Deck.
Let’s not forget that Valve released a Linux port for TF2 in 2012, released their native client in 2013, released SteamOS in 2013 and in the end ported nearly all their games to linux. It didn’t start with Proton.
But Humble Bundle pushed ports before that, because games had to have a Linux port in order to get into the bundle.