uh I have a 2011 macbook pro and I can't install Mac OS big sur, Catalina or Mojave pls help

High Sierra is the highest version possible on a 2011 MacBook Pro.

For verification, if needed, see your model in: Identify your MacBook Pro model - Apple Support

It's either a newer Mac or if you want to keep using it et a safer browser...

Might try this, it's Chrome Browser without google & without Ads...

https://brave.com/

If you need Office Software...

Look into the Free LibreOffice, it handles MS Office files like Word & Excel, & Page Layout…

https://www.libreoffice.org/