If an engine account is set to a different currency than an advertiser, metrics will appear in what currency when scoped to the engine level?
Ad group’s currency
The correct answer is:
Engine account-level reports are in the engine account’s currency. You set this currency in the engine account itself before the first sync into Search Ads 360. After the first sync, any currency changes you make in the engine will be ignored by Search Ads 360.
Read more here: https://support.google.com/searchads/answer/1252624