On How to share files between Ubuntu and OSX? I found these apparently easy instructions on how to connect to my Mac from Ubuntu:
In mac OS, go to System preferences > sharing and enable Personal File Sharing
In Ubuntu open DashHome and open the Files folder. (or however you know how to get to the files folder.)
In the sidebar, choose Browse Network
As long as the two machines are on the same network, your mac should be in there as a directory that you can mount within Ubuntu.
On Ubuntu 20.04 I open Files (also called Nautilus) *> Other Locations,I choose MacBook Pro ... under Networks. Then a window pops up asking for Username, Domain, Password. But no matter whether I use name and password for the Mac or Ubuntu it doesn't work. And what is "Domain"? I tried "Staff" (and "WORKGROUP"). Nothing works!
PS: The Mac is a MacBook Pro (13-inch, Mid 2012) running MacOS Catalina Ver. 10.15.7. It seems to be using SMB for networking.
To connect to the MacBook from Ubuntu I had to use Terminal commands.
The functionality in Ubuntu Files is VERY primitive. I would call it a waste of time... It doesn't give any error messages. It doesn't even tell you that you need to install this: