The EFI PIN BLASTER hardware for brute force.
A Smart iCloud / EFI Unlock Tool for all macbooks and imacs 2015 and olders
The EFI PIN BLASTER is the most advanced tool to unlock iMacs or MacBooks that have been locked with a four-digit PIN number this will not work if have 6 digits. It works on MacBooks, MacBook Airs, MacBook Pro’s and iMacs older and 2015 versions. It uses a brute-force method trying all possible PINs this will take some time but will work. This method will not destroy any hard drive inside or your MacBook, meaning your Mac does not have to be opened. and most important, EFI PIN BLASTER does not void your Mac’s warranty!
this is from rebelsimcard.com/ team, they are working for quite some time using brute force EFI Unlock Tools.
Smart EFI Firmware USB Unlock tool with LCD Display – 4-digit Unlock Code – RECOGNIZES CORRECT CODE
EFI iCloud LCD Smart USB Device Unlock MacBook PRO Air Mini Macs
Running all the 4 digit codes takes about 2 days. All the 6 digit codes 200 days, so this is maybe less realistic.