There's a Professional category for New Game runs (not New Game+).

Professional difficulty is only unlocked after beating the game once. How would you be able to do NG runs on that difficulty if so? AFAIK it's not possible to wipe your inventory/progression to start a new game.

When you do the "New Game" run, it's just supposed to be a run as IF you were starting over again. You can still run it on a file that has beaten the game before (otherwise yeah, you couldn't run pro ng)

All you have to do is spend all of your money, make sure infinite ammo is off (if you have it equipped), have a clear inventory (pretty sure you just have to have nothing equipped on Chris or Sheva, not entirely sure about the storage though. I don't see an issue if you have stuff stored, but just don't use the storage. If you do, make sure the items you would use it for are not present upon starting the run) and use default costumes.

I'd double check with a mod just for safety measures! Hope this helps (or is accurate, it's been a while since I've been here)

I think someone made a custom save file which was technically NG+ and allowed you to play on professional, but only had the starting items, no money, and no unlockables. If anyone knows who made that file or wants to make one themselves, that would be a great thing to add to the resources.