There must be some really obvious trick which has escaped me.
If I favorite a marked location on MacOS Maps, or on iOS Maps, I can’t see how I can give it a custom name.
Tapping or clicking on Info doesn’t seem to help, and I can’t see any other method.
I have tried the technique of selecting favorites from the search bar (in MacOS), selecting edit and trying, but the text remains uneditable.
I would even consider a third party app if there is one.
I am using MacOS Mojave, and iOS 12.