Nobody forces Microsoft to exist in the EU, or to sell their software to EU citizens. They would simply be forced out of that market.
A workaround will be found, or one of the two sets of laws will be changed, or one of the two sets of laws will not be enforced.
I'm not sure how resilient this is to coercion by the US government. Maybe the US government could forbid Microsoft from doing business with the data trustee unless the the trustee gives up user data.
Your shell game you suggest will not withstand the scrutiny of an intelligent judge and an aggressive prosecutor.
Source: A lifetime ago, I was asked as a consultant to spec and site infrastructure out of the reach of the US government with the help of an international law attorney.
While I'd agree that small-ish foreign companies can probably fly under the radar, I don't think any company that receives payments from US customers is immune to coercion from the US. If the US government can impede a company's ability to access US customers then that's an ability to compel a company to give up data.
What imagine will happen eventually (be it in the next couple years or next couple decades) is that agreements along the same lines as free trade agreements and extradition agreements will be made between countries. In exchange for the ability to get data from other countries under certain conditions, the US grants the ability for other countries to do the same. Probably these agreements would be made with other liberal democracies; I don't expect China or Russia to hand over data to the US nor vice versa.