Oh, I see - hard refresh consistently shows HTTP/2 but after one or two soft refreshes it becomes HTTP/3 for me until next hard refresh.

Edit: it is always second soft refresh for me that starts showing HTTP/3. Computers work in mysterious ways sometimes.

I restarted FF and am now seeing something similar. Hard refreshing alternates between 2 and 3, and soft refreshes quickly get back to 3 most of the time