That one payment is legally a tax and another is not has no bearing on whether it is economically a tax, any more than the culinary distinction between fruits and vegetables bears on the botanical one. Botanically a tomatoe is a fruit. In the kitchen it’s a vegetable.

Not sure I can follow you here. What’s your definition of a tax?

I would define it as an involuntary payment, mandated by government.

In German law the insurance contribution may not be a tax because payment of it entitles you to certain services. That doesn’t stop it being an involuntary payment, mandated by the government, a tax by common definition.

That doesn’t make the legal definition wrong, but it isn’t really relevant outside a legal context just as a chef won't argue with a botanist that actually a tomatoe or a pumpkin is a vegetable not a fruit. Botanically they’re right but who cares?

https://en.wikipedia.org/wiki/Tax

A tax (from the Latin taxo) is a mandatory financial charge or some other type of levy imposed upon a taxpayer (an individual or other legal entity) by a governmental organization in order to fund various public expenditures.[1] A failure to pay, along with evasion of or resistance to taxation, is punishable by law. Taxes consist of direct or indirect taxes and may be paid in money or as its labour equivalent.