Can a false pope become a saint?
Step-by-step reasoning process below:
yes
A false pope, or antipope, is someone that tries to claim they are the true pope but the church rejects them.

Hippolytus (c.

170–235 AD) headed a schismatic group as a rival to the Bishop of Rome, thus becoming an antipope.

Hippolytus (c.

170–235 AD) was named a saint in the Roman Catholic Church.

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Therefore, the answer is yes