Cannot Sync iMessage on Macbook Air M2

I'm trying to set up my Macbook Air M2 (Monterey), and it won't download my text messages from iCloud into Messages. It just sits there, saying it's downloading them from the cloud.

One concerning issue is that the "Sync" button next to "Enable Messages in iCloud" is greyed out, even though I've checked the box to enable them.

I've tried logging in and out of iCloud (on this device and others), I've verified that messages are being stored on iCloud (~25gigs of them), I've rebooted the computer several times - nothing. Help!