Hi,
the insider build will only be uninstalled when the next build of Windows 11 comes out.
To stop getting preview builds, make sure your device is in the beta channel.
Then, reboot the PC, and try to unenroll the device from the insider program.
You will still stay on this build until a higher build number for windows 11 comes out.
If you want to get rid of the build right now, you will have to do a reinstall of Windows 11.
Insider builds are not intended for the average user and can also be unstable. You will have to live with the issues unless you want to reinstall.
Regards,
LightJack