If the assignment would take you an unreasonably long time, you simply are not the candidate they are looking for. Shrug, thank them for considering you, and move on to the next interview.

If this happens frequently, you may be interviewing for the wrong jobs, and should consider either something more junior or closer to your core competencies. Or consider upskilling before applying for these positions., to extend your competencies before they ask you to demonstrate them.

If the problem is that they are looking for a superhero who doesn't exist... They are entitled to waste their time looking. It's a pity they waste the candidates' time too, not that is unfortunately part of the process. When looking for an enchanted prince, either as employer or employee, you're going to have to kiss some frogs.

If the assignment would take you an unreasonably long time, I suspect you simply are not the candidate they are looking for. Shrug, thank them for considering you, and move on to the next interview.

If this happens frequently, you may be interviewing for the wrong jobs, and should consider either something more junior or closer to your core competencies. Or consider upskilling before applying for these positions., to extend your competencies before they ask you to demonstrate them.

If the problem is that they are looking for a superhero who doesn't exist... They are entitled to waste their time looking. It's a pity they waste the candidates' time too, but that is unfortunately part of the process. When looking for an enchanted prince, either as employer or employee, you're going to have to kiss some frogs.