Okay, I now know the answer to this for anyone reading in the future: The Austrian Consulate made a mistake. You must contact them and send your passport back so they can fix the visa sticker by adding "ERWERB".
It means that you cannot qualify under that bullet point to enter Croatia. But you can get a digital COVID certificate on the basis of a negative test. Such certificates are valid for 48 or 72 hours, depending on the circumstances. See https://gruenerpass.gv.at/getestet/:
Ich bin getestet.
Wie lange gilt mein Zertifikat in Österreich?
Ein PCR-Test gilt ...