since we are a 2 party system even though we pretend we aren't
De-jure we are a multi-party system. De-facto we are a 2 party system.
If you vote for anyone else other than Biden, it increases Trumps chance to win [...] We know it's not a literal vote for Trump, but it might as well be a theoretical one.
Without splitting any further hairs, yes; that's essentially correct.