Safari extension has suddenly disappeared from Safari and extensions preferences

Safari Version 15.1 (17612.2.9.1.20) is no longer showing 1Password as an extension. The separate app is installed (1Password for Safari Version 15.1 (17612.2.9.1.20)), but it's disappeared as of this morning. No new updates have been installed, but it's gone! Rebooted, deleted and reinstalled the 1Password for Safari app; no difference. Any suggestions? Main 1Password app is 1Password for Mac 8.4.0 80400053, on BETA channel

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1Password Version: 80400053, on BETA channel
Extension Version: 2.1.4
OS Version: macOS 12.0.1