The MFC tooltip handling code has a bug. You can set the width of a tooltip but there is a hard-coded max width for the description text. It’s set to 200 pixels and a little trickery is needed to fix it.
The trick is to add code to mainframe.cpp to do a little extra initialization for the tooltip controls. The code above assumes that the app class is derived from CWinAppEx. I also build two versions of my program and one of them let’s the system scale up the entire window instead of my code handling it.
The value being hard coded is silly at best and negligent at best. The MFC coders did some great work but there’s a few little crap bits in it like that that make things really hard. I won’t discuss the recent Windows 10 update that caused the GetPixel code to be enormously slow other than to say that this kind of shoddy work is fortunately not too common.
If you have the problem, I hope this code helps.
[UPDATE]
I think that there is a tooltip that is not being updated by this code. Hovering over most of the toolbar buttons results in wider tool tip boxes except for hovering over the checkbox controls. Those appear to still have narrow boxes and text that wraps much too soon. Unfortunately, I have no idea where these tool tip controls might be configured and I don’t intend to fix this right now.