I have a 3'x3' patch job and trying to identify this type of texture. Any ideas?

That's tough. I might have guess slap brush but it's not obvious.

Someone on Reddit mentioned using a grocery bag to pull away and leave bigger patterns.

It's this, thinly mixed and rolled on. Going to be very difficult to patch a small piece only and have it match.

As said, good luck matching it. Iv'e tried it before and it was a terribly frustrating experience.

You're better off redoing a larger section if not entire wall, you will never get a small section to not stick out like a sore thumb

Gonna be hard to match exactly but you can get close enough. I've done patches like this in the past and thought it would be a huge deal but then I realized one day my life is filled with plenty of stuff that actually precludes me from staring at the walls and looking for imperfections. How much time you spend idle and staring at your walls will vary by person.

That's what I normally do.

Large nap with watered down mud

Many great ideas above, some even SOP but all avoid - as I assume you also - what an interior designer would demand = redo the entire wall and often in a much different style/color aka Accent Wall.

In redoing HVAC ducts, we had a patch job and eventually it seems to blend in with the rest/original but when new stuck out.