Re: "MacAir doesn't show up on FindMy app": "... my other Apple devices don't show the Mac on the device list"
        Looked under Settings/Account on my iPhone 16 and it shows the Mac but when selected, shows the
       FindMy feature is OFF. How do I resolve?
You may want to :
Check whether the Mac, iPhone, other devices, are all signed in to with the same Apple (ID) Account details. ie: Items not signed into. , or items signed into with a different Apple (ID) Account won't show up in Find My. :You can: Check your Apple Account device list to find where you’re signed in - Apple Support
Check whether some small, but important detail is being overlooked:
Eg: Is Find My Mac turned on in iCloud ?
       See: *How to turn on Find My on your iPhone, iPad, or Mac - Apple Support
       Check if your Mac appears in Find My on iCloud.com  https://www.icloud.com/find
Check whether Low Power mode is in use on iPhone, and if so, try turning it off and check Find My list again.      * Check whether Location Services are enabled on iPhone
                   Restart the iPhone and see if the Find My app updates to include the Mac
                                                              
More Info:  If Find My is offline or not working - Apple Support
              Check for outages: Apple - Support - System Status