How do I change my computer name/identity on all Apple devices?

I am unsure what you mean by “iMac identity”.

Are you referring to the name of your iMac itself?

• Change your computer’s name or local hostname on Mac - Apple Support

Or to the name associated with your iMac login?

• Change Users & Groups settings on Mac - Apple Support

How to change the iMac login short name is linked above. This short name is one of three usernames you can use to log into the iMac, the others being your full name as configured in the iMac Users & Groups, and (usually) your Apple Account. Make absolutely certain you first have a complete and current backup, before changing your short name.)

Or the name associated with your Apple Account. There are several ways to change that name, including here:

• https://account.apple.com

If you acquired this iMac from somebody else and not new and not previously erased, there is a more involved sequence to untangle your ownership from the ownership of the previous owner, particularly if the previous owner did not correctly release ownership of the iMac .

Not sure if this is what you want to do on a Mac

Change the name of your macOS user account and home folder

On the iPhone and iPad go to General>About>Name and change it there.

AirDrop isn't the same across devices.