Is there a rule explaining when a paragraph should start and when a line break is acceptable?

Question

Content

Over the years, I have come across the fact that users are very inaccurate in arranging their texts. Most annoying when single line breaks are abused. Instead of packing finished pieces of thought into paragraphs of several sentences, each new sentence begins on a new line.
Because of this, it becomes difficult to read, the author’s thought is worse absorbed. And for content management and design, this is generally a nightmare: user texts, with their appearance, with their incorrect formatting, begin to greatly spoil the impression of the service. Here's a typical example of this abuse of hyphenation: Is Medium.com readable?
Tell me, is there any rule that regulates in which cases a line break is acceptable, and in which it is necessary to write sentences one after another, forming a paragraph? I searched the Internet and to my surprise I did not find anything similar to such a rule. But line breaks are typical for rare cases: for writing poetry, for indicating direct speech, for displaying a list (and I don’t even know more cases).

Answer 1

There is, and even a lot ... But, I'm afraid, users will not like them, because. the reason for the careless handling of the text lies in the carelessness of thinking, which, alas, cannot be eradicated by any rules :)