Whether racism or not, it's probably an -ism of some sort. Despite disagreeing with the GP, at least their painting of "Karen" as an -ism gave me pause and made me consider that usage again. In truth, it's probably not a great and useful practice in discourse. e.g; do you believe calling someone a Karen will increase your chances of reconciling with them or coming to a favorable outcome with that person?
Food for thought: In the (rough) words of John Mulaney, if you equate something to another word, but you won't even say the other word, then one is clearly worse than the other.
1) Stop capitalising "white". 2) "little old White women are prohibited from attending church" - [citation needed] 3) "popularisation of "Karen" racist dialogue" - how is this racist?
Tyrone is a internet stereotype of a thuggish blackman. The stereotype of Tyrone is considered by some to be racist (probably quite rightly). Karen is a stereotypical entitled white woman. So if calling someone a Tyrone is racist, therefore calling a woman a Karen is also racist.
Not saying I agree with any of it. But that is my understanding of how the logic works.