can someone explain professional mode on facebook?

It's reversible, which most people don't realise - you can switch it off in the profile settings and go back to a normal profile. It also opens up the monetisation tools if you meet the eligibility rules, which is why creators use it instead of running a separate page.

It turns a normal personal profile into something closer to a creator account without you having to start a page from scratch. You get followers rather than only friends, public posts by default, and a proper insights tab. Your friends list and existing posts stay as they are, and you can switch it back off. Worth it if you actually post publicly and want to see what performed. If you use the profile to talk to people you know, it adds nothing.