Good for you to have found the solution. In this stage of your application, may I advise you to have a look at the Base application. You will find a lot of code an functionality that will be of good use to you. And if it is not too late, start over in an application that has better modules than the techdebt-filled ‘Administrator’ module. It will save you a headache or two.
Best of luck with your app!
Based on a couple of other users forum posts I found out what was missing from the ManageMyAccount microflow. Why exactly this solved the issue, I do not know.
But when the MF passes the account object, a create activity, set to the $Account variable needs to be parsed too. Maybe because the create/delete association requires that an image object be created when opening the page… honestly no idea.
The image below, in the green box, is what I added to the MF to get the browse button enabled