I’m searching for a switch that’s ON when it’s unplugged and OFF when it’s plugged. I made a GIF that describes what I mean:
In my example I use a small ON/(OFF) slide switch, which is made to be OFF when it’s plugged. It’s just an example though, it doesn’t have to use a slide switch or look exactly like it does in my example, but it does need to have the same basic function.

 

What are you plugging in a usb lead , ?

 

Are you describing normally on, push off switch? They are reasonably common for turning things off (e.g., machinery with relays wired to stay on once they are turned on) and for emergency offs.

This is just one example: https://www.digikey.com/en/products/detail/c3controls/W22PB-MB-DG/13145944

There are cheaper versions and with smaller buttons too.

 

Most quarter-inch jack sockets have a contact that opens when a plug is inserted.
https://www.rapidonline.com/truconnect-2-pole-pcb-standard-jack-socket-20-1390

 

Or most board PS entry jacks for example.
The plug-detected pin turns off the GND side.

 

Stereo headphone jax that disconnect the speakers are the common example of what the TS wants. What we don't know is if they need to be isolated. That exists also but iit is less common.