The petition only makes legal sense if it were to ask to extend the set of charitable goals as specified in the Abgabenordnung, but the existing set already allows for FOSS projects as part of e.g. the "national education" category (public code is educative).
And, to be frank, I also don't get the "recognition" part. The tangible benefits of volunteering for a charity are limited; what does it even mean to get recognition for it.
It may be educative but that is hardly the most significant way in which open source code is beneficial to society.
Dependent on the project, other categories might work too. The list is in Abgabenordnung §52 ( https://www.gesetze-im-internet.de/ao_1977/__52.html ) / Fiscal Code Section 52 Public benefit purposes ( https://www.gesetze-im-internet.de/englisch_ao/englisch_ao.p... )
(Contrary to intuition, "advancement of science and research" is very hard to get accepted in unless you're a university or at least publish papers in journals. And while the law claims that in theory other purposes could be argued for, in practice tax authorities will simply stick to the list and not make exceptions.)
It would also be a plain and simple category error. The legal code is not concerned with the how. It doesn't list actions but abstract pursuits, outcomes. "Open source development" simply doesn't fit there. My previous comparison was "cleaning toilets". It can equally be part of a charitable activity beneficial to the public if you do it for a charity, yet there would be no point in adding it to a closed list.
By the way, it would still require the project to register as a German charity, file reports, etc.
Plenty of questions, zero answers in the petition. The petition doesn't state what their goal is at all. What is the actionable item, what is the request, and from whom? Even a prayer is usually more specific.
To me, it doesn't read at all like the petition is advocating to add "open source" to the list of charity goals, since that has nothing to do with "getting volunteering recognized" (whatever that may refer to). Charities work with money, which is what the law is about after all -- it's a Tax Code! All it deals with is money. Unless you deal with actual financial flows, you don't need to respect any of that, and you're free to do whatever! "Volunteering" has very little to do with money.
And I say that as somebody who has almost exclusively worked for and with charities, in both paid positions and as volunteer, for the past decades. I really don't know what this is advocating for. I get a lot of "recognition" for my contributions to open source projects, both finanicially and non-financially, and so do others that I know who contribute to open source.
It's like petitioning for "rainbow cotton candy". Sounds nice -- who would object to that! But: Who? What? Where? How?