A PTIN is required, but the Registered Tax Return Preparer progam (and the testing that was proposed) is NOT. The courts have ruled that the IRS can’t enforce it. The current status is that the RTRP designation is optional.
Some states have requirements. I think CA, OR and NY all do.
The only federal requirements are procedural and ethical -sign any return you prepare, keep necessary documentation, comply with Circular 230, etc.
There are some requirements if you want an EFIN, which is necessary to e-file a return. Part of that process is an FBI background check.
This is one reason that the consumer needs to be very, very careful about who they engage to prepare taxes for them. I won’t say that you get what you pay for, but if you don’t see credentials like an EA or CPA, you’re relying entirely on the word of the preparer that they know what they’re doing. Even at a firm like H&R Block, pay attention to the preparer. There are people at HRB with decades of experience who know their stuff… and then there’s the minimum wage newbie with 15 hours of training and the cockiness that comes from not knowing how much you don’t know.