As you said, Linux distros and Postgres both heavily rely on US code. Even Linus has been a US citizen for over a decade now.
Almost all modern hardware those clouds run on, from compute to storage to networking, also rely on US code.
When you think of actual, true, real alternatives that can be used today, every single one of them will have some sort of dependency on the US. Even the homegrown platforms in China, which are already lightyears ahead of EU offerings, remain heavily dependent on US tech. It is just a reality of the globalized market.
So at what level do you actually consider yourself completely sovereign in this realm? The reality is, the EU cannot be at this point in time. Realistically, even decades from now seems highly unlikely, even if they actually made a decent initiative at trying.