To follow up the poster in the linked thread confirmed this works for PC but not confirmed for Mac. I'm on a Mac and as of Oct. 2020 and for OS X 10.14 and 10.15 this doesn't work. There's no language menu on install. Changing all other language menus and updating the preferences doesn't solve joioning/ligatures.
Photoshop, Illustrator, and InDesign support Arabic, Farsi, Urdu, and Kurdish languages as all these uses Arabic alphabets. So whether you're on a Mac or Windows, above mentioned Adobe applications will serve the purpose.
Since you will not be using Arabic all the time, you have two options:
Uninstall existing Photoshop that doesn't support Arabic, they reinstall another version that does.
Install a little older version of Photoshop that supports Arabic alongside existing copy of Photoshop, so you end up with two Photoshop versions on your machine, one for general English, and one for Arabic specifically.
Let me know which option you prefer so I can guide you through. For me, I would suggest the second option for you.