I'm going to open a bug report for this, but also posting here for visibility.
Regardless of how many newlines you type in your actual app review or reply, the store just renders everything as one huge wall of text (with no newlines). This limitation is just ridiculous, because it makes it hard to write a coherent review with paragraphs or a list of issues / steps to resolve a problem. Same goes for review replies.
Also, if you type in a bunch of text in the review input field, but you accidentally click somewhere else, you lose all your work without any confirmation. This is just another example of Garmin's systematic lack of attention to detail when it comes to UI/UX.