Learn Swedish: Konstverket tycks ha tjocka och korta penseldrag. - The artwork seems to have thick and short brushstrokes.

In Swedish, tyckas (to seem) acts as a semi-modal verb of impression. Just like true modal verbs (such as kan or vill), it is followed directly by a bare infinitive. You drop the infinitive marker att, resulting in tycks ha instead of tycks att ha.

Is tycks a passive verb here?

Structurally, it is the passive form of tycka (to think / to hold an opinion), but here it functions as a deponent verb. This means it has an active meaning—to seem or to appear—even though it keeps the passive -s ending.

How can we tell that penseldrag is plural here if it doesn't have a plural ending?

You have to look at the adjectives modifying it. Penseldrag is an ett word ending in a consonant, meaning its plural indefinite form is identical to its singular indefinite form. However, the adjectives tjocka and korta both have the plural -a ending. If it were a single brushstroke, it would be ett tjockt och kort penseldrag.

What is the difference between using tycks and verkar in this sentence?