I see this a lot in localized software. Windows says "Wird heruntergefahren" or "Wird neu gestartet", that is it uses the passive voice, when the corresponding english source uses present progressive - "Shutting down" or "Restarting". On the other hand I see in other apps (volunteer-translated) another form - "Am herunterladen". I've been told that this form "am (Verb)" expresses an ongoing action just like the progressive tenses in english, but the form itself is either colloquial or regional.
To what extent is "am (Verb)" an "official" sort of way to describe an ongoing action and what are the contexts in which it's shunned?
Bonus question: what is this form "am (Verb)" even called? How exactly do you google it?