I think the right move for the EU (which I doubt they'll take) is to do industrial policy by repealing anti-circumvention laws (transpositions of Article 6 of the EUCD), which would allow EU firms to make interoperable components for US tech.
That would mean that - for example - an EU firm could supply every mechanic in the world with a universal car diagnostic kit (replacing the $10k/year/manufacturer that mechanics pay now). These kits could unlock subscription and software upgrade features, so any Tesla owner could stop paying subscription fees to Musk and instead pay a one-time fee to a mechanic (whose tooling comes from an EU company) to jailbreak their cars.
This could be done with app stores - anyone in the world who wants to set up an iOS app store could buy the tools to let their customers switch their iPhones to it from an EU firm.
It could be done with printer ink, med-tech, medical implants, industrial IOT, ag-tech (alt firmware for John Deere tractors, etc).
These are global markets with nigh-infinite upsides. The next national champion is a Nokia, but for the gizmo that lets a guy working from a folding table at the corner shop jailbreak your Xbox and install an alt app-store where the world's games companies can sell their wares without giving 30% to Microsoft. That's a product with a VAST global market, which would create consumer surpluses worldwide (including in the US) and deliver industrial policy that incubates a domestic tech sector to the country where a firm develops it first.
This is also critical for any Eurostack effort. It doesn't matter how many Office365 clones the Commission subsidises: unless EU firms can move all their data (including file permissions, edit histories, etc) out of the Microsoft walled garden and into an EU alternative, they will be held back by switching costs.
There's a huge market (again, worldwide) for fearless, robust scrapers that pull all this data out WITHOUT Microsoft's permission or cooperation. Every MSFT enterprise customer would benefit from the existence of such a tool, even if they don't ever use it, because the mere fact that you CAN costlessly leave Microsoft at the click of a mouse means that Microsoft has to fight for your business.