"Text tag 3d can handle text with multiple lines just fine. If you're entering the text yourself, just put a carriage return in the text panel; if you're building the text to display from some data, use "string join" with a panel…"
"TextTag3d xcalls a Rhino internal text drawing method with a single string. Normally "\n" should be coding a CRLF in the string. Since this this doesn't break the line, TextTag3d seems to be for a single line of text only."