I mentioned the last time a 3rd party candidate was able to make a dent was Ross Perot, and that's because he was super rich and could buy access to the kinds of campaign activities and press that most people would need to fundraise or be "connected" in order to get
(Perot bought prime time major network timeslots to do what were, in essence, infomercials for his campaign.)
I could see Elon doing something like that for whichever candidate wanted to run for his new party. Heck, the guy spent $40B to buy a social media platform because he didn't like having his posts blocked...so this kind of endeavor certainly wouldn't be his most impulsive purchase by any means.
As far as the vote splitting, that would depend on who he "anointed" to be the "chosen one" to be the candidate for his new party.
Andrew Yang has already reached out to Elon to collaborate on this "new party" idea.
If, in 2028...
We saw a Gavin Newsom vs. Andrew Yang vs. JD Vance election showdown... I don't know that anyone can accurately speculate who an Andrew Yang type person would steal more votes from.
At the very least, he's got the money to get whoever his candidate is significant airtime and on the debate stage, and that's a sizeable portion of the battle.
Imagine if Ross Perot had been 20 times richer than he already was, and owned something as powerful as his own social media platform