Hi GraymatterSTM,
Welcome to Apple Support Communities! We're glad you've reached out for help with this issue enabling Find My on your Mac. Let's work it out together.
To start, let's ensure that your computer is updated to the latest compatible version of macOS. Which version does it show under Apple menu () > About this Mac?
Here's a guide to help:
Update macOS on Mac - Apple Support
Have you had a chance to restart your Mac since noticing this? If not, here's a guide to help:
Log out, sleep, wake, restart, or shut down your Mac - Apple Support
Next, if the issue persists, head into System Preferences, click on Security & Privacy, then click the Privacy tab, and ensure that the option for Location Services is enabled.
Then find System Services in the list, and click Details. Make sure that the checkbox next to Find My Mac is selected.
Afterwards, return to the main System Preferences window, click Apple ID, then click iCloud. Select the checkbox next to Find My Mac.
Let us know if this helps, or if you've got any questions.
Have a great day!