According to Steam's own survey, Linux is still less than 2% of the user base and it doesn't look like it's changing much. I don't know how it has looked historically though but probably not too much different.
Realistically speaking, it's only a small percentage of people who bought the Steam Deck, and they probably already had a gaming PC, which means they probably had a Windows PC.
So unfortunately, I don't think Linux gaming is anywhere close.