What is the difference between the dairy products quark and skyr? What is the difference, if any, between the two dairy products quark (consumed in German-speaking countries) and skyr (traditional in Iceland)?

They are both similar to what the result would be if you took cottage cheese and blended it.

I'm interested in any differences in the contents. I read the Wiki articles I linked to. In Britain skyr is labelled as yoghurt (at least the Arla brand is) and must therefore contain both Lactobacillus bulgaricus and Streptococcus thermophilus. Wiki mentions both in their skyr article and neither in their quark article, where they mention lactococcus instead. But I don't take Wiki as canon and I wouldn't assume that these and only these bacteria are included.
Stiftung Warentest, a famous German consumer protection agency, actually tried to answer that question and even had trained food testers try to determine the difference in taste. The result was basically that Skyr is very close to lightly beaten (Mager-)Quark, but with a higher acidity closer to traditional Yoghurt than traditional Quark and with a higher calcium content.