You can't upload a .apk now it must be only .aab
It depends on the IDE you are using. I still use Flash Builder 4.7 for my awesome game.
I am still tweaking some stuff but I had a few puzzling questions like you for my game.
Just follow the instructions in Harman Air SDK release and you should be fine.
The forum has a lot of Q&A I found lot's of answer's here.