I'm going to tell the story of landing my first professional commission, mostly because I wish someone had told me how unglamorous it was.
I posted a piece of fan art on Twitter that got moderate traction — a few hundred likes, nothing viral. Someone in the replies asked if I did commissions. I said yes, quoted a price I had roughly calculated from looking at other artists' sheets, and got a yes without negotiation. The piece took me about eight hours. I was underpaid but not embarrassingly so.
The actual work was the easy part. The hard part was the communication: interpreting a vague brief, managing revision expectations, delivering files in the right format. None of that is taught in any art course I know of.
If you're waiting until your art is 'good enough' to take commissions, stop waiting. The skills you need — client management, deadline keeping, professional communication — only develop through doing. Start with lower stakes: friends, small community work, things where a mistake isn't catastrophic.