Not talking about comics, rather on books (like actual novels containing chapters consisting of only words). They say that both French and German are “closest” to English but still different languages, however even if an English speaker were going to learn either language, does it mean can they understand written text from books or is that hard even with cognates?
It depends on the genre of the reading material, also affects difficulty regarding vocabulary. Such as: thriller (crime): has terminology, uses expressions and bundled in sentences that are beyond A2 level proficiency while YA (teen) may be written within a beginner lens. This is not the same as reading a sign in French as a English speaker as books have blocks of text.
Even in the reverse: what is the recommended level (from A1-C1+) for a non native who is learning English as a second language to read an entire book (like those written by Lee Child, Agatha Christie) fluently with understanding not only the contents written but infer on the novels concepts and relay reading comprehension akin to a native speaker?
Not 100% an answer to your question, but I was able to start reading reading Japanese fantasy novels around mid-B2 while using a dictionary and likely could’ve started earlier at the cost of more pain (and it was already plenty painful). Neither other language I speak is even remotely close to Japanese, so you can put lower B2 as an upper bound. With that in mind I could see upper B1 if the languages are close like in your example and the subject matter is on the simpler side, but A2 ain’t happening. At that point you’ll struggle too much to understand the grammatical expressions in the text to comprehend the subject matter.