I guess your US LLC doesn't have an operating agreement.
You should draft one stating that your friend will be the manager of the company.
The real question is "
will PT accept this"?
The answer is, in theory yes but in reality nobody knows because as i said in my first post Portugal doesn't go after non residents.
That's why nobody bother with hiring managers, because nobody know if it's something that could actually help in case of an audit.
If you want to make things by the book and be prepared even in case of a very unlikely audit but still pay 0% tax then use a Singapore non resident company managed from Malta.
Why Malta?
Read about
resident non domiciled companies.
The Singapore company will not be tax resident in Singapore but resident in Malta because of management and control but if you don't remit anything in Malta, Malta will not tax you.
Portugal will se dividends coming from a Singapore company and you'll receive dividends tax free under NHR.
Both solutions work, obviously the running costs for the resident non domiciled solution are higher because you need one nominee director in Singapore because it's required by the law and one in Malta.
With the US LLC there's only you managing the company directly.
Finally you could also mix both structures making the Singapore non resident company the single member of your US LLC so that all the US LLC income will flow through the Singapore company managed from Malta and you'll get diviends out.