Howard Miller

Well...

sudo apt install php8.1-mysql

It's only a change to php.ini if you're using Windows. Which you clearly are not. Otherwise, you need to add the mysqli extension. How you do that depends on how you install PHP in the first place. 

Something like 'sudo apt install php-mysql' most likely.

There may be some javascript trickery....

BUT... if you REALLY don't want users to be able to access pages after logout (for whatever reason) you are probably going to be disappointed. The pages are stored by the browser and not by the server. The best thing you can do is to ask your users to log out and close the browser. However, it's difficult enough to even get students to log out

"Vulnerability"?

I'm not seeing the vulnerability. What potential problem are you trying to fix?

Many student-facing file upload screens allow the file types to be restricted. However, it's still only looking at the extension.

Yes - I am aware of that