Want to leave Xbox insider but cant

You'll want to try posting over on the Insider Reddit to see if Insider staff can assist - https://www.reddit.com/r/xboxinsiders/

Open the Insiders app on your Xbox and make sure you're not a part of the Xbox Omega beta testing

My console doesn't appear there but states it's in the program. I didn't use my account to add it. Is that why?

Thats Correct. The account that enrolled your console into the program would need to login to remove that console from the program.

Go into the Insider Hub app and side scroll to the settings section, then Manage Devices, and de-authorize the console from the program. Keep in mind, this will remove you from the program and also remove all Insider updates. As such, your console can
auto default back to its original settings which is the same thing as doing a complete factory reset. You will need to re-install your account and all digital content onto the console once you boot it back up. When I left, it took a few days before the console
reverted itself back to factory defaults. Good luck!

My console doesn't appear there but states it's in the program. I didn't use my account to add it. Is that why?

Go into the Insider Hub app and side scroll to the settings section, then Manage Devices, and de-authorize the console from the program. Keep in mind, this will remove you from the program and also remove all Insider updates. As such, your console can
auto default back to its original settings which is the same thing as doing a complete factory reset. You will need to re-install your account and all digital content onto the console once you boot it back up. When I left, it took a few days before the console
reverted itself back to factory defaults. Good luck!