A thing hasn’t reached another Mac

Check both Macs

• The same Apple Account. Both Macs must be signed in to the same one.
• iCloud Keychain on. In System Settings, choose your name, then iCloud. Your pouch’s key travels in iCloud Keychain.
• Online. When a Mac is offline, its panel says so, and its changes wait until it’s back.
• Room in iCloud. If your iCloud storage is full, nothing new can go up. The pouch in the menu bar shows an amber dot until there’s room again.

Give it a moment

iCloud usually delivers a change within seconds, and now and then takes a few minutes. Carriel also looks for changes when you open the panel and when your Mac wakes, so opening the panel on the other Mac is a good nudge.

See what Carriel says

In the Carriel window, Settings › iCloud and Macs shows whether this Mac is up to date with iCloud, and lists your Macs with when each was last seen. A Mac that hasn’t been seen for a long time may be off, asleep, or signed out of iCloud.

On a new Mac

A Mac that joined a moment ago can take a while to receive iCloud Keychain, and Carriel can’t tell “on its way” from “turned off”. See Moving to a new Mac.