Learn Swedish: Rynkorna, dem försöker hon dölja. - The wrinkles, she tries to hide them.

This is called left-dislocation. We pull the topic (rynkorna) completely outside the main sentence for strong emphasis, and use a pronoun (dem) inside the sentence to point back to it. While Rynkorna försöker hon dölja is perfectly correct, adding the extra pronoun makes it sound much more natural in spoken Swedish and puts a heavier spotlight on the wrinkles.

Why is the pronoun dem used here instead of de?

Because the wrinkles are the object of the sentence, meaning they are the thing being hidden. Even though they are brought to the front of the sentence, the pronoun replacing them must reflect their grammatical role. Therefore, we need the object form dem. The subject doing the hiding is hon.

How does the V2 (verb-second) rule work with the comma and the extra pronoun?

The dislocated word Rynkorna sits entirely outside the main clause, so it doesn't count toward the V2 rule. The main clause officially begins with the pronoun dem in the first position. To satisfy the V2 rule, the verb försöker must immediately follow in the second position, which pushes the subject hon to the third position.

Is this comma-and-pronoun structure common in formal writing?