He did not sign any such thing. He signed a bill that added some new language to already existing law. The part about forced vaccinations was already there. It was not part of any bill that he signed into law. Here is the law as it existed in 2018 when he was running for governor:
Florida Statutes 2018 - #4 in the list includes the forced vaccination language
In 2021, DeSantis signed legislation to make it clear that forced vaccinations are NOT allowed in Florida.