After a Monterey update: for the guys trying "System Preferences" -> "Accessibility" -> "Pointer Control" -> uncheck "Ignore built-in trackpad when mouse or wireless trackpad is present", and finding the box was never checked in the first instance, using a USB mouse or bluetooth trackpad, check the box. Reboot and using the USB mouse or bluetooth trackpad, uncheck the box and reboot again.
Built-in trackpad was working again for me.
Extreme-Gardener
Users receive reputation points by contributing quality content to the forums.
Posts include post and replies published on the forums.
Post authors can mark replies as Accepted to indicate successful solutions.
Apple Developer Forums admins can mark replies as Apple Recommended to indicate an approved solution