Any way to pin a web page or document to the menu bar for quick reference?

I am a bit confused. What I think you are looking for is to have a pop-up/drop-down/whatever window that displays the contents (only, not the editing tools) of a Google document? Doc only, or sheet, etc. too?

I use SwiftBar (formerly BitBar) for something similar. I wrote a primitive plugin (bash script) that displays the current date in YYYYMMDD format in the menubar, and when clicked, in the dropdown is a link to open NotePlan to today’s note, and beneath that, the contents of that note (just using cat to show the raw .md file, piped into echo for line breaks). If you are linking to a local static file, it could be something as simple as

echo “—”
cat /Users/yourname/file.txt | while read line; do echo ${line}$para; done

Showing the contents dynamically would involve some API calls to google, and you’d need to find some way to retain formatting if that’s important.

Yes, exactly. But it doesn’t have to be a Google doc. Could just be plaintext, rtf, or pdf.