Hi,
On MacOS, Ancestris.app is not a binary file that accepts command line parameters. So what you are trying to do will not work, and using "=" will not work either anyway. MacOS command lines are the same as Linux.
To launch Ancestris with a specific java pah, change the jdkhome variable in the user settings folder.
The file is in /Users/<yourname>/Library/Application Support/ancestris/trunk/etc/ancestris.conf.
To see the Library folder in the Finder, you need to press Command+J. It is hidden by default.
In the ancestris.conf file, change the jdkhome variable removing the # sign in front of the line.
See the doc here:
https://docs.ancestris.org/books/user-guide/page/java-installation#bkmrk-cas-de-macosCheers,
Frederic