Upvote:2
No. If the anti-Christ were to become pope, all that would mean is that the anti-Christ is the pope.
There have been numerous valid, bad popes throughout history. There were popes in the middle ages who were siring children out of wedlock and giving nepotically handing out high positions of authority in the Church. There have been popes who taught heresy, albeit unofficially, as they are unable to teach heresy officially due to the power of the Holy Spirit.
If a valid pope is on the chair of Peter in Rome, he can be the worst sinner in history or the holiest saint. Either way, the chair isn't vacant. A bad bishop is still a bishop. A bad pope is still a pope.