OS update capability on older MacBook Pro

If it it is Late 2013, it can run the current macOS version OS11 "Big Sur:

Otherwise you can upgrade as far as 10.15 "Catalina" with the link in this Apple article:

How to get old versions of macOS - Apple Support

⚠️ HOWEVER....

IF you have older versions of critical and/or expensive software, like Office 2011 and older, or old versions of Adobe Creative Suite, they will not run on any macOS version higher than 10.14 Mojave.

You can use this free app to see what older apps you have and if there are upgrades available that will make them compliant with Catalina or Big Sur:

https://www.stclairsoft.com/Go64/

In in doubt, don't upgrade higher then 10.14 Mojave until you get it sorted.

Some Users running versions OLDER than 10.11 El Capitan discover experimentally that they must install 10.11 El Capitan as a waypoint before going further.

El Capitan includes a more modern App Store than can make even later versions much easier to obtain and install.