If Prevost and his VII predecessors are legitimate popes than you MUST submit to their authority and all the doctrines they promulgate.
So get out your felt banners, give the sign of peace, and join in with the LGBT pride mass, or worship the great thumb...because it doesn't really matter, everybody goes to heaven.
1) A legitimate pope and legitimate commands/authority are 2 different things.
2) A pope can be legit in holding the human/govt office, but be non-legit in holding the spiritual office.
3) A legit pope can give illegitimate commands.
4) A legit pope does not have unlimited authority.
5) etc, etc
The papacy is not a simple office, nor are it's powers simple, nor is it's authority unlimited. It's quite complex, as this crisis has shown.
If a heretic pope was easy to explain, it wouldn't have taken St Bellarmine 5 opinions, nor would it have absorbed the time/energy of St Bellarmine and all the top theologians for multiple decades of study, research and debate. An effort which STILL did not lead to a consensus or an easy explanation.
Your overly-simplistic, either-or narrative simply ignores many aspects of the papacy in a desire to reach a quick answer that the modern, muddled, lazy mind can swallow.