It may be a result of personal preference, but I struggle to see how talking through challenges encountered with a personal project are a poor indicator of competence. If you ask some boilerplate list of questions, sure, but few if any candidates could memorize all of the random in-the-weeds architecture questions one could ask while talking through someone's project. For a junior specifically, even a non-answer to these questions provides valuable insight into their humility and self-awareness. I also think that it'd be pretty easy to visually weed out personal projects created for the sake of saying one has personal projects, like a bootcamp may push to create, versus an actual passion project, and even easier to weed out during any actual discussion. I suppose YMMV, but in my experience, the body language and flow of discussion are vastly different when someone is passionate about a subject versus not.