When did your LO start sucking their thumb?

My daughter is currently 4 ½ months and LOVES to eat her hands. She was a big fan of pacifiers at first, but started accepting them less and less when she discovered her hands 2 months ago.

For the last week or so, she's been refusing it entirely in favor of her fingers. Not her thumb, not her hand, it's specifically her 2 middle fingers lol. Any time she needs comfort, decides she's ready to sleep, etc, she pops her middle and ring finger into her mouth, tucks her thumb into her palm or points it outward, and leaves her index and pinky fingers sticking straight up on her cheek like 🤟 Sometimes it seems like she's determined to gouge her eyes out 😅

It didn't occur to me until a few days ago that most babies are probably sucking their thumb by this age, and now I'm wondering if she ever will. She seems perfectly content with those 2 fingers and has basically zero interest in her thumbs (she loves mine though!)

Do all babies learn to suck their thumb at some point? When? Is there any reason I should be discouraging this weird finger obsession she has?