Try this. Don’t know if it works on all computers.
Your computer has a Notepad - and when you copy a text you can paste it into the Notepad first, and then copy it from there before you paste it elsewhere. Notepads remove formatting.
Could be related to the fact that HTML doesn’t have normal line breaks, but rather uses <br />.
Though you would think the browser would be smart enough to grab those when you copy and paste.
In most browsers you can right click, do something like “inspect element” on what you desire, right click it in the html browser that pops-up and choose to copy the actual html block. You could then paste it into notepad or elsewhere and do a search for <br> or <br/> or <br /> and replace it with an actual blank line.