Looks like your symlink is a finder alias and not a symlink. OSX Finder handles both of them the same way, but at system level the finder alias is a plain file.
Substitute the finder alias for a proper unix symlink using ln -s command and it should work.
Emacs 26.3 knows connection-local variables. Your approach is OK. However, you must set the :user property explicitly, like
'(:application tramp :protocol "scp" :user "myname" :machine "my-linux-host")