Cambridge

Is it true that 30% of students don’t meet the step requirement for Cambridge and still get in

I'm assuming you mean for Maths, in which case it's slightly higher, usually around half:
In 2024, 537 offers were given out and there were 260 acceptances, so ~51% of offer-holders missed their offer (or chose not to go).
In 2023, 524 offers were given out and there were 258 acceptances, so ~51% of offer-holders missed their offer (or chose not to go).
In 2022, 537 offers were given out and there were 252 acceptances, so ~48% of offer-holders missed their offer (or chose not to go).
In 2021, 528 offers were given out and there were 233 acceptances, so ~56% of offer-holders missed their offer (or chose not to go).
Note that a significant portion (I think it's about a third) of Cambridge Maths students missed their STEP offer and Cambridge have access to the papers and scripts.
I also wouldn't worry too much if STEP seems difficult at first. It is a difficult exam but it has a technique to it and is definitely doable with practice.

I think the op is referring to missing step offer (slightly, I presume) but still going to cambridge (maths)