Is Sedevacantism heresey or schism?

Hello,
I was speaking with a revert in the faith about this and was wondering if Sedevacatism is in schism or heresy. I didn’t want to say either when I wasn’t sure. Thanks for your help.

Heresy is the obstinate denial or obstinate doubt after the reception of baptism of some truth which is to be believed by divine and Catholic faith.

Schism is the refusal of submission to the Supreme Pontiff or of communion with the members of the Church subject to him.

Sedevacantism refers to groups that refuse to acknowledge the Pope as legitimate, and therefore would fall under schism. They could also contain heresey but primarily their driving force is a refusal of submission to the Pope and the canons of the Church.

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