But those are standardized too, and definitely not something a builder would demand you buy.

Usually you buy a house/apartment here, and then you buy a kitchen separately, and they ask you if you want a standard oven or a built-in one, and they leave a hole for either... I guess you can buy an oven with them too, and they install it, but you can definitely buy any standard sized one, and just screw it in, eg:

https://www.mimovrste.com/pecice

https://www.mimovrste.com/i/17170441/550/550 <- example diagram

You also need a separate cooktop for the builtin variant, but they can cut out a hole for that too (sizes are pretty much all standardized)

A lot of people still use standalone ovens+cooktops, eg: https://www.mimovrste.com/stedilniki/gorenje-kombinirani-ste...