I think that's what the EU is probably hoping, but all they are going to do is mandate themselves into paying a shedload more money for a lesser product
Let's assume I'm Amazon and I provide "cloud". My intellectual property, what defines "my" cloud and makes it better (or worse) than MS or Google is how I create and manage my cloud, the tools, the processes, the procurement etc
Now I'm told I can only provide "my" cloud, if I actually agree to give away all that IP to a third-party that I'm only allowed a minority stake in - a huge risk given that this is exactly how countless technology firms have had their fingers seriously burned when trying to operate in China
The only possible way to do that is to retain a minority stake and license my IP to the other cloud provider at an extortionate rate. Now there are two "Amazons", my own native product un-certified, and a new certified product running exactly the same tech (or maybe a "lite" version), just with a badge that says it's somehow more secure and for three times the price.
However, in exactly the same way as it has done for other areas of technology and defence, all this takes to unravel is a US edict forbidding any of the three to license their cloud IP to overseas third-party providers on the grounds of US national security - in fact right now they are probably actively lobbying the US behind the scenes to do exactly this.
So with that, yes you might get your "ringfenced" EU cloud, working in exactly the same way but for a ton more money, and very probably in some kind of "cloud-lite" mode.
So the EU governments and probably their various procurement teams will be mandated to use it, and all it will achieve is to cost them more. As we've seen with several high profile leaks from the US, you can have all the vetting you like, all the firewalls and security you like, and be sitting wherever you are instructed to sit, but if you want to leak info, you're gonna do it anyway, regardless of whether your platform has a pretty little logo attributed to it, and any "backdoors" hidden away in the system are going to be duplicated into the system you are licensing anyway. The EU majority owner of the JV won't actually develop anything in house as they will have to license in the whole platform, and those license fees will be fed back to the US companies anyway, thereby making them even richer than if said EU governments just licensed their normal product, and the majority owner will effectively be nothing more than a reseller
Pure protectionism, the eurocrats will claim a victory, and one way or another the EU's citizens will pay way over the odds for a what will very likely be only a marginal increase in "security".