Cannot recover device PIN for a MacBook Pro after "Mark as Lost" in Find My on iCloud.com/find

I lost and recovered my MacBook Pro in airport Lost & Found. But I cannot find the PIN used to lock my MacBook. Following online manual trying to recover the PIN through iCloud.com/find. The online manual is here: Mark a device as lost in Find My on Mac - Apple Support (IE)

However, iCloud.com/find does not show option to unlock this MacBook. When clicked in this MacBook, it shows "play sound" (tried and it worked), grayed "Lock" button, grayed "Erase Mac" button (screenshot with user name redacted). How could I start the sequence to recover the lost PIN on iCloud.com?