Can't upgrade past High Sierra

I have a MacBook Pro (Retina, 15-inch, Mid 2014) running High Sierra (10.13.6). I'm trying to upgrade to any of the newer versions of OS. I understand this mac is not compatible with macOS Monterey, but it should be compatible with macOS Big Sur.

The Updates section of the App Store does not have any OS upgrade options, it only lists "Incompatible App Updates"

I followed the instructions here (https://support.apple.com/en-us/HT211683) to upgrade to an older OS, but when I click the link under "Use Safari to download macOS on your Mac" for any of the OS options, the tab says "Connecting to the iTunes Store..." and the App Store opens up to the front page. No sign of an OS download.

I can't find any of the OS when searching in the App Store. The only OS I find in the App Store is Monterey, which is incompatible with my mac.