There is also third party recruiters for specialist positions such as IT, Law, etc. who are often the only entry point into a particular firms open positions.

At their best you used to be able to actually speak to them and they would go find a job for you. They would help you tailor your CV and cover letter to suit, prep you for the interview, etc. They are typically paid by the hiring company a significant percentage of your salary in installments if you get hired. You can pay for this service now, but getting a good one is hard.

I used to get direct contacts from them for positions that actually matched what I can do for a salary that would actually match what I am after. They used to have an actual industry knowledge and contacts.

Now, at their worst they spam people on linkedin with connection requests for positions that are completely unsuitable, AI has made this far far worse now. They often use a ghost position just to farm CVs for future positions, totally counterproductive if you wanted to tailor your CV for a position.