Probably nearer 0%. These stats are from browser user agents on select sites. The chances that large amount of people are visiting these on their steam deck will likely not be very high. And there is only like 0.5% of people using the steamdeck on steam ATM.

The Steam Hardware Survey puts Linux at 1.44% (though gaming is heavily skewed towards windows users). And 0.57% using the AMD VANGOGH graphics card (which is apparently what the steam deck uses).