Yeah it's pretty simple: there's a lot of moderate conservative voters who don't like Trump
Then by your judgment, would it be a mistake for the GOP to nominate him again?
It would probably depend how Biden's term goes. I imagine that if the economy recovers and the pandemic ends, Biden, or his successor, can run on successfully cleaning up Trump's mess and reminding Americans about what happened the last time Trump was President and how bad things got. It's possible that Trump's reputation finally gets the due condemnation that it deserves at that point and makes him damaged goods for 2024.
Then again, when the country is in a stable point under a Democratic administration, American voters rarely ever reward Democrats for it and instead elect a Republican who squanders that stability, requiring for a Democrat to succeed them and clean up that mess. It's a cycle that never seems to end.