microsoft office 365 issue with MAC 10.11

You can upgrade to Mojave 10.14.6, or to Catalina 10.15.7 on a mid-2012 MacBook Pro. Use only the Safari browser with those links. Because Catalina accepts strictly 64-bit applications, some of your older applications may not be supported without 64-bit compatible updates by the respective vendor, or replacement applications with comparable functionality. Use the free, Go64 software to determine which applications are 64-bit and those that are not.

Never perform an upgrade with less than 25 GB of free storage remaining on your Mac that you determined from performing a Get Info on your startup drive icon on your Desktop. Never perform an upgrade without first running a Time Machine backup on the existing installation, and I also prefer to boot into Recovery and perform a Disk Utility First Aid on the boot drive before an upgrade.

Exactly what model Mac do you have?

A 5 year old Mac Laptop should be able to upgrade all the way to Catalina.

So it's not 5 years old, it's 8 years old...

As noted above, you can upgrade all the way to Catalina if you want.