A necessary commonality across all possible ways of thinking?

It would be great if there is a way to refute this school of thought but I have come across none that I thought were satisfactory. The Pyrrhonean skeptics seem to have made the least disagreeable premises for their argument they could possibly make. Generally, as I understand it, the argument goes like:

P1: One must presuppose a premise to make an argument (like right now)
P2: There is an infinite number of presupposible premises
P3: There is no way to know the truth of a presupposed premise (by definition, it is presupposed)
P4: Sufficiently different premises lead to different conclusions
C: There is no way to know the truth of a conclusion for certain

Now, this goes back and applies to itself, so P1/2/3/4 may be doubted as presupposed premises and I am asking how that may be done. It seems to me that P1/2/3/4 are too elementary to be doubted and so the skeptic conclusion must follow.

Is there a premise that must be accepted apriori by all schools of thought equally that is NOT P1/2/3/4? If so I would really like to know what it is.

Similarly, is it possible to dispense with any one of P1/2/3/4? Wouldn't the act of doubting premises as elementary as P1/2/3/4 just be a demonstration of how C still stands no matter what? In the act of doubting such elementary premises, you'd only be demonstrating that any premise is doubtable