ShareMouse can synchronize locking and unlocking on multiple Windows PCs and Macs*:
If any computer is locked, all other connected Macs and Windows PCs are locked as well.
A security count-down allows you to cancel any automated locking.
How to sync lock/unlock
Install the ShareMouse software and enable lock/unlock synchronization in the settings on all computers. The ShareMouse software then runs silently running in the background.
Whenever any computer is shut down, ShareMouse shows a count down on all other computers and shut them down after the grace period.
So much more than syncing locking and unlocking
ShareMouse does not only sync locking and unlocking but also allows you to share the mouse and keyboard of any computer with any other computer on your desk:
Automatic login is not available on Macs running macOS Catalina