So I thought I start an activity and keep track of my expenses during a US trip. I have a local US$ account and spend in dollars overhere.
After I created an activity, I cannot add expenses made in dollars as it says it’s impossible to add different currencies than the activity which seems to be default in Euros. So it looks like you cannot use the activity to handle US$ payments.
Now maybe our local support assistant in NYC (Ali 😉) can have a lookout it in his spare time. Otherwise you can not keep track of expenses while outside the eurozone which is a pity.