Schwarzenegger would be a walk-in, regardless of which party he gets behind him.
There is a parallel reality where Democrats pushed hard to change the eligibility rules during Obama’s second term, selected Ahnold, and continued the Obama legacy of slow-going, moderate social progress. Sadly we are in a darker timeline.
Arnold took a political beating from both sides when he failed to accumulate the capital to push any of his ideas through, and the experience appears to have left the governor with no enthusiasm to continue.