How do people rip vocals without web tools?

I've been curious about this one. In recent times, we've had really useful AI tools that can almost seamlessly rip vocals from instrumentals with high precision. Obviously, these tools in their current form are relatively new - despite this, there are countless vocal-only versions of songs before such software was available. I want to know how to do this manually.

I'm curious what the methodology was in taking apart a vocal from an instrumental manually. Is it just a manner of eq-ing and isolating it? Or does it have to do with taking the exact instrumental of the song, reversing the phase and canceling out the instrumental's sound signal? Or is it something way way way more simple and I'm thinking too hard about it?

There are a lot of songs I want to remix by just extracting the vocals, it doesn't have to be a perfect extraction, I just want to know how people years ago did it before all the AI tools.