To calculate the chance you have to do:
1/5444517870735015415413993718908291383296
What follows is pedantic, I know, but for the sake of accuracy this isn't
quite correct.
First of all, a 12 word seed phrase converts in to 132 bits of data. Indeed, 2048
12 (which I assume is the calculation you did) equals exactly 2
132. However, the last 4 bits of this number are not random - they are a checksum. This means that only 1/16th of all 12 word seed phrases are actually valid, and a wallet will never generate an invalid seed. So the denominator for your fraction is "only" 1
128, rather than 1
132. Furthermore, we can't calculate the numerator for that fraction. If you were looking to have a match with another
specific wallet, then yes, the numerator would be 1. But if we are looking for a match with
any wallet with coins in it, then we would need to know exactly how many different wallets there are holding coins, which of course, nobody can know.
As I say, this is all pedantic, because the bottom line is still the same - it is impossible.
Now, to be even more pedantic, there is theoretically no limit to the number of addresses that can be derived from any single BIP39 seed phrase. If you were to take any seed phrase and derive enough addresses by adding an arbitrary number of branches to your derivation path, you would almost certainly end up with a collision at some point. Practically though, we would reach the heat death of the universe before you even came close.