Current questions and answers regarding the map editor.

Will a map created in version 1.6 work in version 3.1?

Yes, it should.

Please tell me, is there an editor for macOS, and if so, where can I find it?

No, definitely not. There isn't an official one, and fans are unlikely to create one. Possible solutions:
1) Install a Windows emulator.
2) If you don't need to edit the landscape, you can use an archiver that supports zip archives, meaning you can unpack the map and manually edit everything in a text editor.