A serious third party appeal from the never-Trump Republicans in 2024? Entirely possible. Less so if Trump is not pick of the GOP litter at that point, but if the frontrunning nominee apparent at that time looks to be a down-the-line Trump advocate, it's still a probable scenario.
It would be even more interesting if in 2024 a mantra that began like "anybody but Trump" --again-- turned out to be "anybody but Trump or Biden". The anti-Trump conservatives probably hope to be able to pull in some blue dog Democrats to improve chance of defeating a Trump or wannabe-Trump so they're not going to be running a hair-on-fire right winger. They'll be appealing to someone who in comparison at least looks far more mainstream.
An unexpsectedly appealing third party run is not without precedent, of course: in 1992, the pop vote swings weren't concentrated enough in electoral-vote geography when Ross Perot put an actual fear of voters back into both parties, racking up 19% of the popular vote, even while not taking the EV in any state. But it sure God woke up the honchos in both parties, particularly because Perot came in first in some counties in six or eight states, and in some of those areas garnered as much as 40% of the vote.
Not sure when the younger generations right now are going to pull the plug on the entrenched power structures in both major parties, but 2024 might be a remarkable on-ramp, the way things are going.
The gen Z are six years older and wiser than they were in 2016, and they were getting fired up already about what a messed-up set of circumstances the boomers and silent gen are leaving them and their slightly older compatriots to deal with.
"There is always one moment in childhood when a door opens and lets the future in."
--Graham Greene
The trick is for the Gen Z all to turn up at the polls and vote. The truth is that their American lives depend on their doing exactly that. Otherwise it might not matter how they would vote down the road, if the Trump-hijacked GOP eventually has its way with rigged courts supporting laws overturning unwanted election results.