Probably "unlimited" in the same way that visa-exempt air entries already are "unlimited".
No legal limit, but after 4-8 months (give or take) on nothing but back-to-back border bounces, you have a *high* chance of being pulled out of line to the back office & questioned about what you're doing here.
If you have a visa, there is no land entry limit (though if you've already been here multiple months on short-term tourist stays, you run the risk of being questioned or even denied).
There is a legal limit of two *visa-exempt* land entries in a calendar year.
So to clarify; your 4 land entries:
1) Were they all visa-exempt?
2) Did you make them before or after Jan 1st 2024?
If you've been here 4 months, six months, or longer on nothing but visa-exempt entries, just going out then straight back in, however, then the likelihood of an immigration officer viewing your history as "extensive" goes up several notches.
Technically they can insist on 20K B in cash. They may do exactly that.
However, last year I was pulled aside at the airport and asked for the Three Proofs, and a copy of my Thai bank book was accepted. (I had already had to show it in KL to get the visa in the first place).