If you notice that there are missing extensions for Safari macOS, even by restarting the app and the Mac, you have come across a bug introduced with macOS Big Sur and which is apparently not fixed. with macOS Monterey. It may happen that the new generation web extensions, those based on the WebExtensions standard and which have been added to Safari 14, are no longer active in the Apple browser and especially that they are no longer visible in the settings of the app. If necessary, a detour via the terminal is mandatory, as developer Jeff Johnson points out on his blog.
I encountered the problem with the latest version of Safari and macOS Monterey, several extensions disappeared after restarting the Mac, including the new one from 1Password which can work without installing the full app, or the one from Bitwarden. Legacy extensions, based on tools provided by Apple before Safari 14 and which remain available, were still active and visible in the browser preferences.
To get everything back, start by quitting Safari. Then open the macOS Terminal with Spotlight, copy this line and paste it into the window. Validate by pressing the key
↩︎ and reopen Safari. Normally, all extensions will be visible again in the browser preferences and you can reactivate them.
/System/Library/Frameworks/CoreServices.framework/Frameworks/LaunchServices.framework/Support/lsregister -f -R /Applications/Safari.app
However, this command line removes website permissions for all extensions based on WebExtensions. Concretely, you will have to authorize each extension again to give it access to all or part of the websites. It’s restrictive, but it’s a priori the only option to find these extensions.