Learn Dutch: Hoewel de mythe beroemd is, is hij ongetwijfeld nep. - Although the myth is famous, it is undoubtedly fake.

Ongetwijfeld (undoubtedly) is a sentence-level adverb of evaluation, meaning it expresses the speaker's judgment about the whole statement. In the middle field of a Dutch sentence, these adverbs typically go right after the finite verb (is) and the subject (hij), but before a predicative adjective like nep.

Why does the second half of the sentence start with the verb (is hij) instead of the subject (hij is)?

This is due to the verb-second (V2) rule. The entire subordinate clause (Hoewel de mythe beroemd is) acts as the first block of information in the main sentence. Therefore, the main verb (is) must immediately follow it in the second position, which forces the subject (hij) to swap places with the verb.

Why do we use hij (he) to refer to a myth?

Mythe is a de-word. In Dutch, you use hij to refer back to most singular de-words, even when they are abstract concepts or inanimate objects. You generally only use zij/ze if the word is explicitly feminine (like a female person or an inherently feminine noun).

Is nep an adjective or a noun here?