How to make a block only appear for a certain content type?
This can be done in a few ways.

If your content type always has a unique URL (such as /news) you can set the block to only show when on a page matching that URL.

Or this can be managed in a variety of ways using different plugins that allow for the manipulation of displaying content types and their corresponding views/blocks.

Are you currently using any plugins like that or have any themes installed?