Dropdowns are only appropriate if the quantity of choices is large and the user already knows what the choices are, and then you should be able to type your selection in. This would be things like birth year, country, and state/province.
Otherwise you add extra clicks, extra scrolling, and visual search of a brand-new element that can't be evaluated ahead of time.
Large, but not too large. You might think this is a silly objection and no one can get that one wrong but I actually have an example: I once worked for a company with a six digit number of employees and they introduced a new ticket system for company wide support. This was some years ago and also the transition from a dedicated desktop software to a browser based web UI.
Someone had the idea to make the ticket number selection a drop down, which looked nice in testing and a few hours after production roll out, but the fun ended quickly - with thousands of tickets it was completely unusable within a day.
https://technology.blog.gov.uk/2020/02/24/why-the-gov-uk-des...