Can you upgrade memory in a 2019 MacBook Pro?

No. RAM and storage (two different things) are fixed at production.

You can use external drives and flash drives for extra storage.

If you are talking about onboard RAM , no...

it could have been upgraded at the time of purchase

but that’s it

jb

otherwise go with what macjack wrote

If you mean "This webpage is using significant memory" that's the fault of the website. They are probably generating a lot of content, images or videos and/or getting content from many different locations around the world.

You can try this:

Quit Safari. Turn off Extensions Safari menu > Preferences > Extensions. Delete Internet Plug-ins from Safari. Clear Safari History, Cookies and Cache.

Thanks for stepping in, sir.

I have advanced mind reading skills. I also never heard of Pages.app using significant memory. :)