https://bugs.winehq.org/show_bug.cgi?id=53598
--- Comment #4 from Nikolay Sivov bunglehead@gmail.com --- (In reply to VZ from comment #0)
In Wine 7 MDI child windows show strange icons in their title bar (looking like "0", "1" and some strange rectangular shape, respectively) instead of the expected standard minimize/restore/close buttons.
Frame button glyphs are supposed to come from Marlett font that wine provides. It sounds like for some reason your installation can't access it, and is using some other font that produces digits instead of symbols.