Altcoins is mostly determined by the btc price movement and the season may not affect every altcoins pump. I'm recent time, precisely t.from early this year, 2021, some altcoin has been experiencing their seasons. Check out ethereum, it has been braking records and creating new "All Season High, while we see some altcoins at the coiarketcap, stagnant.
As a matter of fact, altcoin season is determined by the ntc price movement at all time.