upgrade to montery

That's a late 2013 model, which can't be upgraded past Big Sur.

(262539)

For your late 2013 MacBook Pro, Big Sur OS 11 is the highest possible.

what model-year macBook pro?

apple menu > about this mac

(please don't post your private serial number)

Big Sur is still enough to run current versions of

• The Firefox Web browser
• The LibreOffice office suite
• The GNU Image Manipulation Program (GIMP)
• The Affinity Studio suite (free with registration, as long as you don't need the AI features. Those require a paid subscription, a Mac with an Apple Silicon chip, and Ventura or higher)

However, if you need Monterey (or higher) to run applications from a vendor who no longer supports Big Sur (such as Microsoft or Adobe), the only upgrade available is a "forklift" one. I.e., buying a new computer. With the speed at which technology changes, 12 years is a pretty good run for a laptop computer.