cannot update MacBook Air to Monterey from Big Sur

I have a Macbook Air (11-inch, Early 2014) currently running the latest version of MacOS Big Sur (as of the time of this posting) 11.7.1. I am regularly getting on-screen notifications that MacOS Monterey is ready to be downloaded and installed, but when I click the notification (or manually navigate to System Preferences -> Software Update), the only message I receive is Your Mac is up to date - MacOS Big Sur 11.7.1. This has been going on for months now - since MacOS Monterey was first made available to my machine. I get a notification that Monterey is available, but then there is no option to actually update and the Software Update window doesn't show that Monterey is available. I have had no problem with Big Sur updates during that time, and I am constantly able to keep my Big Sur version up to date, so there isn't a problem with the update service in that regard. Any ideas?