Mission Impossible? how to copy an iOS App from old iPhone to Mac and to new iPhone

[space-time]

yes, I figured out I do not want to update to 12.7

I am still with 12.6

There is an option "File -> Devices -> Transfer Purchases from iPhone" but that does not do anything, despite making sure iTunes and iPhone use the same Apple ID account.

I rememebr when I saw ALL my Apps in the left side, now it is Empty. I managed to add 2 Apps there that I had on my local hard drive but I cannot add Apps from iPhone. It seems like iTunes can upload Apps to the phone, but it cannot download Apps from the phone, which is what that "File -> Devices -> Transfer Purchases from iPhone" is supposed to do.