I don't see a specific rule for this, but I would just let them ignore the restriction of picking a certain number of archetype feats before selecting a new archetype. There's nothing preventing you from picking a 2nd level feat at level 4.
Pathfinder 2e General Discussion
I would just let them ignore the restriction of picking a certain number of archetype feats before selecting a new archetype
That seems reasonable.
There's nothing preventing you from picking a 2nd level feat at level 4.
I realize now that my question was a bit ambiguous, but I was specifically talking about the bonus feat slot from the variant rule.
Playing with free archetype almost inevitably requires making house rules to accommodate it. You level 4 issue can actually start at level 2, as there are sub-classes that can grant a multiclass dedication feat as a class feature, and at least 1 racial feat that can grant a multiclass dedication.
Yeah good point. It wasn't top of mind when I made this post but elves and rogues are another big blind spot.