The only way to accomplish this at scale is to build something that is legit better and let the market decide. Anything else is just principled wishful thinking.
Microsoft Teams "won" entirely because it was given away free with Office. Even though it is acceptable these days, it was horrible when it started. There is no way it could have won without unlimited backing from a bigger force.
You have to see EU trying these things in the same light.
I'm unsure the EU could build and require anything worse than Teams, considering the open source landscape for that product category, for example. The primitives exist, scale them up and lock out US companies from the EU market with policy. Recycle the capital internally, just like VC funds do with their portfolio companies.