Find My Mac not working

When local settings show Find My Mac as ON but your Apple Account device info reports it as OFF, the Mac has likely lost its sync handshake or Secure Enclave / background daemon registration with iCloud after the macOS upgrade.

How to Fix the Desync

• Check System Services explicitly: Go to System Settings > Privacy & Security > Location Services. Scroll to the bottom and click Details next to System Services, then ensure Find My Mac is toggled ON (not just the master Location Services switch).
• Full Re-enrollment Sequence (in this exact order)
  • Go to System Settings > Apple Account > iCloud > See All and toggle Find My Mac to OFF.
  • Restart your MacBook completely.
  • Sign completely out of your Apple Account (System Settings > [Your Name] > Sign Out).
  • Restart your MacBook again.
  • Sign back into your Apple Account, navigate back to System Settings > Apple Account > iCloud > See All > Find My Mac, and turn it ON while approving the location prompt and entering your admin password. 
• Verify Multi-User or Volume Glitches: If you have multiple user accounts or test volumes/partitions on this Mac, verify that Find My Mac wasn’t accidentally enabled on a secondary profile (which turns it off for others).
• Check via Web: Log into iCloud Find Devices from another device or browser to see if the cloud service registers the Mac there, as the local UI on another device can sometimes suffer from a visual caching delay after major OS updates

More from Apple: Set up Find My on Mac - Apple Support

I cannot replicate the issue you describe, Find My is working normally on my Mac running 27.0.1. It shows as ON in the list of my devices on my Mac:

When I go to Find My on my iPhone, it appears in the Devices list, with the location shown.

did it work?

Same issue