Marco-Aquamarine-Turtle My advice is to check the website of the specific rental company before you’re planning to book a car there. If it’s a big brand like Sixt, make sure to select the country specific website because the rental terms vary. They usually explain in detail which kind of cards they are going to accept for the security deposit. And I’ve seen embossed being mentioned in these terms and conditions before.
Large banks in the US, Citi, Chase, ... they all started to issue flat cards a couple of years ago even for their premium credit card products, so it shouldn’t be a problem in industries where credit cards are very common and tourists from all over the world book services.
But I would be skeptical with smaller local rental companies. They’re sometimes weird.