Certain reimbursements/allowances for volunteering are treated favorably for tax purposes if conditions are met, e.g. ehrenamtspauschale (volunteer allowance).

Also, as Gemeinnützig, for tax and for issuing donation receipts.

It could also function as community service hours ordered by a court (sozialstunden).

Stuff like that.

In addition to tax stuff there's a card you can get in most states, issued by cities/districts based on certain criteria, like doing a certain amount of hours per week of volunteer work, that will give you a discount or free entry to museums, pools, movie theaters, events.. There's listings online of all the institutions and businesses that give a discount.

Though the petition is about Germany, in the US some entitlement programs come with work requirements that can be satisfied by volunteer work. Given the tech job market and how the US government's labor policies are detrimental to native workers, allowing them to keep their skills sharp through open source work while also satisfying the work requirements of various social programs, it seems like a decent trade-off. This presumes the government and the donors to the politicians that run it don't really want native workers to be unskilled. Their actions indicate the opposite, so that throws a bit of a wrench into things.

Tax exempts (I'm not a German, but I was curious about the same and this is what ChatGPT told me :) )