Interesting.

Not
in
markdown

(Pressed Shift+Return after every word.)

Not in markdown.

But it works in other word processors (like Word, libreoffice) that distinguish between line breaks and paragraph breaks.

Example: Type

Once upon a midnight dreary  
While I was pondering, weak and weary  
Over many a quiant and curious volume of forgotten lore  

To get:

Once upon a midnight dreary
While I was pondering, weak and weary
Over many a quiant and curious volume of forgotten lore

(You can highlight the source code to find the extra spaces at the end of each line). Note that this is different from paragraphs, which add spacing between them:

Once upon a midnight dreary

While I was pondering, weak and weary

Over many a quiant and curious volume of forgotten lore

Once upon a midnight dreary

While I was pondering, weak and weary

Over many a quiant and curious volume of forgotten lore

This is how markdown works. There is no way to disable that. This is an old convention from when text editors didn’t wrap lines automatically and enables you to write long paragraphs of text, breaking the lines as it makes sense to you, without creating a paragraph each time.

See the Lemmy help page on markdown or the Markdown Guide.