This sounds like you may have a corrupt preference file somewhere - perhaps deleting ~/Library/Preferences/co. On a normal install, you'll only be asked to enable on major OS releases. Since you're also on an old version of Catalina it'd be a good idea to install the security updates, too.

You could try to delete all of the preference files:

    find ~/Library/Preferences/ -iname com.apple.siri\* -delete