Here is my code:
As you can see, TeX Studio doesn't recognize the proof environment. Nonetheless, I have activated the amsmath package in the preferences:
So why isn't it working? I have tried restarting the PC to see if it would load the package but it didn't work.
I am using the ProTeXt packages. The output file looks fine.
You're actually not describing the problem correctly. When TeXstudio fails to recognize an environment, it is the \begin and \end that are highlighted red. For example if I add an environment foo, I get this:
The "unrecognized command" popup comes from hovering the mouse cursor over \begin. (Sorry, it didn't show up in screenshot.)
The problem you're facing is a different one: that you've used math mode-only code outside of math mode. The proof environment does not start math mode. And TeXstudio tells you that this is the case:
I just saw that you're using $$ ... $$ for displayed math. Don't do this, use \begin{equation*} ... \end{equation*} or \[ .. \] instead, see Why is \[ … \] preferable to $$?
amsmathdoesn't deal with theorem-like environments, that is whatamsthmdoes. Try activating thecwlforamsthm.\usepackage{amsthm}already, no need for more than one. But I think I realized your mistake. Theproofenvironment itself is recognized (not highlighted in red), but the thing is that it is not a math environment. To use math inside aproof, you need e.g.$...$for inline math, or analignenvironment for multi-line math with alignment.