According to GIMPS, this is the first time a prime number was not found by an ordinary PC, but rather a “‘cloud supercomputer’ spanning 17 countries” that utilized an Nvidia A100 GPU chip to make the initial diagnosis. The primary architect of this find is Luke Durant, who worked at Nvidia as a software engineer for 11 years
Many encryption algorithms rely on the assumption that the factorizations of numbers in prime numbers has an exponential cost and not a polynomial cost (I.e. is a NP problem and not P, and we don’t know if P != NP although many would bet on it). Whether there are infinite prime numbers or not is really irrelevant in the context you are mentioning, because encryption relies on factorizing finite numbers of relatively fixed sizes.
The problem is that for big numbers like n=p*q (where p and q are both prime) it’s expensive to recover p and q given n.
Note that actually more modern ciphers don’t rely on this (like elliptic curve crypto).