The EU commission already sponsors FOSS software, directly and indirectly ( bug bounty programs), so it's really not hot air. Also some EU countries, like France, open source a lot of their code ( e.g. the French government SSO is on GitHub).
The language is vague because it's a generic policy to follow, not "Portugal will replace all MS Office with LibreOffice". That's how policies work, they're generic guidelines to follow.
VLC and 7zip are among the projects sponsored, so you're just spouting nonsense which you could have easily verified.
And again, various EU countries open source software they've created, or data they have for that matter ( open data). Your contemptuous pessimism is fully unwarranted.
When software is developed in house in public administration, then open sourcing it, in my mind, is kind of a no brainer, because it was financed with the taxpayer's money. If they keep it as a "trade secret" it most surely won't maximize value creation throughout society. They're probably not going to spin it out into a government-owned for-profit entity that competes in the market. (Might be interesting if it generates a lot of profit that relieves our tax burdens, but it really doesn't sit right. There are probably laws against that sort of thing. Also: Free markets). So that really only leaves open source / open data as the only viable path.
The real question is: What sort of circumstances drive a government to develop something "in house" that they'll later open source, or adopt an open source solution, when that competes with giving the government contract to your industry cronies.
It would be real nice, if we could get a clear policy framework that basically just says: Whenever open source is an option, the government must go with open source. But we are far away from anyone in power clearly calling for that.
And we've seen some real setbacks where that is concerned: For example the city administration of the city of Munich had that policy in the late 00s / early 10s, to the point where they had migrated 15000 workstations to Linux in 2013, shaving €10M/yr off the Microsoft tax.
All it took was some government officials getting frustrated over a glitch in the e-mail server once in 2017 and compatibility issues about MS Office vs OpenOffice and they reversed course and decided to migrate everything back to Windows by the end of 2020. (It definitely had nothing to do with Microsoft moving their German headquarters to Munich in 2016, if you're naive enough to believe that). -- Don't know the extent to which that actually happened.
As I'm researching this right now on Wikipedia [2], I'm seeing that apparently the new government decided to reverse course back to open source in 2020. -- Don't know the extent to which they've actually finished/begun anything here.
I've also dug into European funding schemes that maintainers of open source projects can tap into for their own living expenses in recognition of their contribution to open source. -- That is incredibly thin. You'd have to be a maintainer of a superstar open source project if you want even the minutest chance at a one-off stipend of up to €50k.
Compare that to how science funding works: I travel extensively in circles of people who do EU-funded science projects and many of them will readily admit that they are downright embarrassed by how little value they create in return for that funding that they get from the EU. These science projects quickly run into the millions, even when they are quite small projects, and the total budget at the government level is quite considerable. When compared to that, the money that they sometimes throw at open source seems like a symbolic amount at best.
The language is vague because it's a generic policy to follow, not "Portugal will replace all MS Office with LibreOffice". That's how policies work, they're generic guidelines to follow.