This certainly depends on local rules. For example, in the UK I believe dental businesses can only be opened by a qualified dentist. I was surprised when I learnt this earlier this year.

This source [0] says “non-dentists cannot set up or buy dental practices as an individual or partnership but they are permitted to be shareholders of a limited company which owns the practice” and “the majority of directors of that limited company cannot be non-dentists”.

[0]: https://www.plutopartners.co.uk/post/who-can-own-a-dental-bu...

I believe this is the case with law firms, and probably some other professional firms, in the US as well. AFAIK a law firm is a partnership of lawyers.

That said, this isn't what most people are talking about when they are talking about starting a business.