I want to help you but I can't because you keep writing things that have no meaning. Multidex has nothing to do with any issue that you encounter.
The next step is to start a new thread and explain what exactly isn't working. And if you include Multidex in the description then I won't be able to help you. Sorry.
Sorry, but how can I explain what happened?
Forget multidex for a second
I opened the project with v12 and it did not compile, I was recommended to add multidex: true and it then compiled, without it it failed
Mind you I did not change a bit only v12
So what other thing can cause it?
This is a very 'old' app working for years like charm, just upgraded to v12 and this all happened
I don't mind to remove multidex but then compiling fails
I do add it the won't update
This is the issue