trying to obtain source code for a particular website using pop OS 21.04

ask the maintainers, or check the website, probably documented (which engine is used).
Otherwise what is your goal? What do you want to achieve at all?

A Web site or a single web page?
You can download any web page to your hard drive either with your browser (<Ctrl>-<S>) or via e.g. curl or wget:
That is the source code of that page.

You can also download many websites with wget. Not all though since javascripts and php are a different story in that scenario.

While you can download complete sites with wget, that's arguably not the "source code of the site", just the code of all its pages.
It really depends on your definition of "site" - it could mean "the software running the site".
OP didn't clarify and possibly didn't put too much thought into their question anyhow.

Javascript is client-side scripting, so ALL of it should be openly available - usually in additional links inside the HTML page, just like e.g. CSS. It's often minified/obfuscated, but if you know how to read it you should be able to completely reconstruct the page in question.

PHP is server-side scripting and is and will always remain completely opaque to the client.