PIN code to unlock Mac

Are you encountering this screen?

Refer to If your Mac doesn't start up all the way - Apple Support:

"Your Mac asks for a PIN code when it has been remotely locked using Find My. Enter the four-digit or six-digit passcode to continue."

If you can't unlock your Mac, refer to this excerpt from If your Mac is lost or stolen - Apple Support:

If you can't unlock your Mac

After you locate your Mac, you can unlock it by entering the passcode that you created when you locked it with Find My.

If you can't remember that passcode, you have three options:

• Sign in to iCloud.com/find, then select your Mac from the Devices menu. Select Unlock and follow the steps to verify your identity.
• Unlock your Mac from your iPhone, iPad, iPod touch, or Apple Watch using your device passcode.
• Take your Mac to an Apple Authorized Service Provider along with your proof of purchase.

Here’s what to do https://support.apple.com/en-us/HT202860