In Florida, the major parties, the only ones who have presidential primaries, have complete control over which candidates appear on the ballot. See this article about the eight Republicans who will be on the Florida Republican presidential primary: Ryan Binkley, Doug Burgum, Chris Christie, Ron DeSantis, Nikki Haley, Asa Hutchinson, Vivek Ramaswamy, and Donald Trump.
The Republicans let anyone who paid the party $25,000, and who promised to appear at a statewide party rally. Also anyone who did not appear at the rally could get on with $100,000.