It most definitely didn’t used to be, historically a “Karen” was someone who would give people who work customer service a hard time. The whole aspect of “Karen” was created to allow retail workers and other customer service personnel a way to vent about a customer, etc.
Over time, various groups began picking up the term “Karen” and started putting down women in general. Often using it as an attack on feminism activists when they become passionate. Once it was picked up outside of customer service circles it morphed into this misogynystic term today. For the most part, it’s still used for its intended purpose but rude dudes weaponized it to attack people in a derogatory way.