The spoiler effect is a real thing when the third option affects two first options that oppose each other. The disadvantage of the 2 party system is that it degrades over time towards two major parties that are the exact same thing in everything but taste, which is the case now in the US: Democrats and Republicans are the exact same thing at all levels except the spice, for Dems taste like woke and Reps taste like cons. That's it, that's all of what actual differences boil down to right now. The exact same thing happened in Argentina, where the two major historically opposing parties became the exact same thing in all but colour. At that point, what you have is one single party that plays as two to stay in power forever, and that breaks the spoiler effect thesis, because the new "third" party is actually the new second one. Again, the exact same thing happened here in Argentina, and that allowed Milei to win with a completely new "third" platform that quickly rendered as the actual second option opposing the fake 2 previous "different" options, and the 2 party system simply reconfigured like so. That's what Milei did and what Elon will just replicate. Do not forget that the vast majority of the US population is uninterested in politics, and Elon can easily capitalize on them and become the first majority if he does a good job.

Trump is essentially a third party candidate

Ross Perot played spoiler in 1992

Teddy Roosevelt allowed Wilson to win in 1912