Can't update MacBook6.1 to OS X 12 or later

I am trying to install an app from the App Store, but I am getting the error message "We could not complete your purchase. (null) can't be installed on "Untitled" because OS X version 12 or later is required."

My MacBook6.1 is currently running OS X 10.11.6. I went to the App Store to update my macOS, but there are no updates available.

How can I update my MacBook6.1 to OS X 12 or later?

Additional information:

• MacBook6.1
• OS X 10.11.6
• App Store error message: "We could not complete your purchase. (null) can't be installed on "Untitled" because OS X version 12 or later is required."

Steps I have already tried:

• Checked the App Store for updates to macOS, but there are none available.

What I am looking for:

• Help on how to update my MacBook6.1 to OS X 12 or later.

Thank you for your time and assistance.