Police unions aren't the same thing as other unions. Most unions exist to equalize labor negotiation through collective bargaining, and police unions tend to include and align with the leadership in the organization that a union would traditionally be negotiating with. In practice they're a lot more like a military contractor than a union (in that their role is to prevent public accountability)

> Police unions aren't the same thing as other unions

What about California teachers’ unions? European notaries?

This is correct and the proof is that police do not strike with labor they fight labor on behalf of capital

The core premise of a union is that you have solidarity primarily across unions which is actually how you get collective-bargaining at larger scales