The problem with bookkeeping is it’s a bit of a dime a dozen and most people/companies aren’t willing to pay much for a bookkeeper as there are a lot of people that can do it and it really brings no value to the company. Most small businesses can do it themselves it’s so easy, so why pay somebody else? If they are looking for bookkeepers, they usually go with local reputable companies that offer bookkeeping services, so building your own client base is very difficult.
IF you can find clients, and that’s a big IF, it’s probably a decent side hustle as you can largely do it from home, it’s easy and usually doesn’t take much time. That being said, expect to be paid quite poorly as bookkeeping is really an unqualified skill, anybody can claim to be a bookkeeper. As an accountant myself, bookkeeping as a side hustle is something I’ve been interested in also, but finding decent clients was the hard part. Most are cheapskates wanting to pay a pittance under the table.