I cannot update my MacBook Pro

The App Store Updates page only informs you of updates available for the OS you are running.

Installing a newer OS is called an upgrade.

Which OS you can upgrade to will be governed by which model and year your mac is.

Click on the  top left of your screen click on About This Mac to find out the year of your mac.

As your profile states you are on macOS Catalina your options are Big Sur or

the newest OS Monterey.

For macOS Big Sur,

Open Safari and click on this link, 

https://support.apple.com/en-us/HT211683

Go to to the use Safari to download OS section and click on the macOS Big Sur.

Before upgrading make a full back up of your Mac.

Check that third party apps you use have updates available for the new OS.

https://roaringapps.com

Check that your printers/ scanners etc have updated drivers and software available for the new OS.

Connect your mac to your router via cable rather than rely on WiFi.

Do not use your mac while it is downloading

and do not use any other devices that share the same internet connection.

If the App Store says ‘Open’ then it is detecting a previous download of the install app

go to the Applications folder locate Install macOS ******.app.

Move it to the Trash, empty the Trash.

Restart, click on the link again, the App Store should say ‘Get' or 'Download'.

If you want to or are able to upgrade to Monterey open Safari and click on the link below,

How to upgrade to macOS Monterey – Apple Support (UK)