It depends on the state. If it’s a purple state or a state where they do ranked-choice voting, then this is right and a vote for Biden is helpful.
If OP is in a solid red state, he can vote for any alternative candidate and it won’t matter which alt candidate he chooses since Trump will already have it locked up.
The only asterisk is if abortion is on the ballot as a statewide measure. That can take a red state (like Kentucky) and turn out enough voters to temporarily make it blue.
I was under the impression that the OP wanted to vote tactically, but if that isn't relevant in their particular state, then they should vote their preference.
Since RJK is an unhinged anti-vaxxer and conspiracy theorist, I would suggest voting for Biden, since it may move the needle for future elections.