How about enforcing direct control about Microsoft business? Not just another “low” fine in the ten to twenty billion range. Just stopping Microsoft, Apple, Google, Facebook and Amazon.
Enforcing AT&T to not enter any new business worked well. In consequence we got UNIX, C, open-source and documentation and finally the TCP/IP-stack of BSD, GNU and Linux. This had a positive effect for the complete computing industry and society. Reagan relaxed all rules, allowed AT&T to split up - the results were bad. No IT company had to fear any regulation afterwards, either politics didn’t want regulate or didn’t understand computing at all.
We don’t need this companies with too much power using incompatibility, vendor lock-in and storing away our data (the newest approach).
Chances for regulation Europe seem a little better? Less lobbyists and less tax money involved and people don’t believe in capitalism. Too late (10xtimes) and too little but at least they react.
EU cannot tell Microsoft in general what to do.
Indeed, the AT&T case at the US is the textbook example, it's worth looking at it.
Microsoft already lost this case twenty years ago? Repeat offenders do not get the mercy of the courts.
Which is why Bill Gates personally intervened, when Munich switched to Linux a couple of years ago.
Enforce the kernel team must be separate from the application layer - let other people build operating system UIs on top of the kernel.
For the operating system team to be separated from the product teams.
Even go further and unbundle the product teams - make office separate from bing which is separate from edge, etc.
Just make sure you also do it to Apple, Google, etc.
This is what the US almost did in the 90s.
And after some (hard) years of actual competition benefits of compatibility will lead to lower prices and more choices.
Regarding Munich: Three competing IT-Departments! Repeat, three. An own special distribution. They didn’t migrated all applications (either do it or not) and a lot of stuff was always done on Windows. Finally Microsoft moved a headquarter to Munich and solved it with “tax money”.
Rumors say that the reverse migration to Microsoft itself was also “bumpy”. Let me guess, three IT-Departments?
The former major of Munich also gave an interesting interview about the “experience”.
A mere split up will lead to “baby bells” and the bigger one will just buy others - and centralize again.
PS: We should remember that Microsoft was able to destroy Nokia with an installed CEO (Stephen Elop) of their own. Killed the already shipping Linux smartphone. Installed Windows Mobile and Nokia was finally dead. Nokia itself did mistakes before but from outside this was questionable?