My iPhone 16 pro max is not recording on photo mode .

Have you tried a forced restart? 

Force restart iPhone - Apple Support

This is different from a simple Power Off. I had to continue holding the button down past the "slide to power off" message, and then I released the button only after  the Apple Logo appeared indicating a re-start. 

If the suggested forced restart does not help, what exactly is the problem? Can’t you shoot photos anymore, or can’t you record video while in photo mode by sliding the “trigger”-button up, or is there something I am missing?