That's a convenience feature for some people who want to be able to take a picture quickly. Unfortunately the implementation is also phone-specific, so I can't help based on my devices (my current phone has nothing like this, my previous one allowed you to put a camera shortcut on the lock screen but you could also just not put it there, and none of my phones has ever had a fixed shortcut).

I'd suggest looking through your settings, especially the privacy and security options, to see whether there is an option to disable this. For Assistant it might also be worth looking at its settings for anything related to using it with the screen lock (I have a vague memory there are some settings related to that, but as I keep Assistant completely disabled I can't look to see).

The alternative may be to look in the Play Store for a third party replacement lockscreen app, which you can set up without such shortcuts.

 

Also try see if you have App Shortcuts in the Lock / Security settings. That applied to a Samsung S9