Not at the moment, a current limitation is that menu-items have to fit on one line, unless they are lists which work like a submenu, so you would probably need to create an extra TextMenuItem and insert it into the dialog. The summary is that to keep the performance drag of calculating items as low as possible the height is calculated upfront. So if you need two lines (or even more than that), just add suitable extra menu-items to the dialog. Menu Items are very lightweight, so it should not make a noticeable difference to your application.
https://www.thecoderscorner.com/ref-docs/tcmenu/html/class_text_menu_item.html
and
https://www.thecoderscorner.com/products/arduino-libraries/tc-menu/menu-item-types/editabletext-menu-item/ (EDIT correct URL)
Also, copy into buffer must only be called after show(), otherwise, it takes no effect.
You can format any menu item using the theme API discussed in the documentation, this allows various justification, formatting, spacing, and fonts, but not multi-line.
You could put in a feature request on the tcMenuLib for allowing multiline formatting, but it would need a lot of thought in how it was handled, and if I'm honest, we probably don't have the capacity to add it in the near future.