I've been using Linux exclusively for ~14 years now. Heavily gaming on Linux only for the last ~8 years.
It was possible (though sometimes headache inducing) to play most games back then (Wine and soon Proton to thank) the biggest change IMHO came with SteamPlay since it turned the headache into one click on most games (thanks to the amazing work of wine/proton developers and the tinkering of the community).
When the SteamDeck released people seemed surprised at the breadth of games that were running on day one. To me it was not really a surprise since I had been Linux gaming with SteamPlay all the time and was almost expecting games to "just work" (though I still would and still am checking ProtonDB before purchase).
What the SteamDeck changed in my view was
- Showing "everyone" that Linux Gaming is a thing that's happening and been happening for a while. So maybe check it out?
- That a Handheld that doesn't have to work around Windows but uses a purpose built OS just makes a lot more sense
I feel that the SteamDeck with SteamOS has really put Linux, especially Linux gaming on the map. Even though I want to be like "Linux Gaming has been a thing forever, I was doing it before it was cool" ;) I have to recognize that fact. In the past years I've seen so many people setting up Linux especially by the way of SteamOS (using HoloISO, Chimera ...) just to play/mess with it which is also why I think an Official SteamOS release will make a huge difference.
Tl;dr: Gaming on Linux was a thing before. But the SteamDeck/SteamOS 3 made a huge impact nonetheless.
Why no K&R?
/s