Can a Florida apartment complex force a renter to pay the rent by auto debit?

What do you mean by force? If that's a term of the lease and that's not what you want to do, don't sign the lease.

I find nothing that says this practice is illegal.

They can make that one of their terms, if you don't wish to rent from them, you do not have to.
They may make it one of their required terms. There is no late payment for them.

If you already have a lease, they can not change it in the middle of your lease