Math – What is the probability of randomly getting a 12-word seed phrase with the same word repeated 12 times?

That’s not correct.

Remember that the last word has a checksum for the remaining 11. This means that any word from 2048 will not work.

actually just 190 words That is, in a universe of 2048^12 possible phrases, only 190 are possible, so the probability is 190/2048^12.