Have you tried:
Or use this link to open the macOS Monterey page on the App Store: Get macOS Monterey. Then click the Get button or iCloud download button.
Which specific model and year Mac do you have?
ALso one user today said:
I was having the same problem. I followed Mal-S's suggestion and deleted Bitdefender antivirus. I restarted, went to software update in preferences, and the option to download Monterey 12.2 came up within a few seconds. Monterey is downloading now without any hiccups so far.
https://discussions.apple.com/thread/253621307?page=1