Do you need to know music theory to be a bar singer?

You can search here. There are many answers, so I won't go into details.

Nowadays, there is a wide demand for talents, so there are naturally many applicants and the competition is fierce. Recruiters will naturally raise their requirements. If you apply for a singer in a bar, you know a lot about music. It shouldn't be difficult for you to learn some music theory. Basically, you can pass those bosses by buying a few books (it's hard to say whether the boss is professional or not)

I wish you success, come on!