Using classic Outlook for Windows in business environments
Instead of deleting the json files in that folder
C:\Users<Youruser>\AppData\Local\Packages\microsoft.windowscommunicationsapps_8wekyb3d8bbwe\LocalState\Migration
I just edited all those files' values from whatever codes there are to "F_ck" (of course the real word, not a masked one). Then I edited those files to be "read-only". Now it has stopped auto installing.
Hope this helps.