Yeah, the most important takeaway is that Teams doesn’t behave correctly when pasting from a plaintext-only clipboard – it doesn’t matter whether it’s our beloved Notepad++, or microsoft’s own notepad.exe, or any other texteditor on the market that I know of, which put the text into the clipboad: the fact that Teams doesn’t behave properly with plaintext clipboard is 100% a Teams problem.
I think we’ve given enough things for the original poster to try to get around their problem, so they can continue to paste from Notepad++ through something else into Teams.
At this point, if the OP has any more questions on other things to try, they should really go to a forum dedicated to Team or MS products or general computing.
(In case my original statements weren’t clear, when I said “the issue is not a problem with Notepad++” and “we are not a Teams support forum”, that was supposed to be interpreted as "and thus, any further Teams-specific followon does not belong in this forum, as it is off topic.)