The icon (a question mark knockout in a black diamond) is VERY fuzzy (at least it does in Windows.) Is it the Unicode Character “�” (U+FFFD) at a fontsize that isn’t supported? Or is it an image that is scaled up poorly?
The 2nd sentence also gives an overly scary warning:
If you upgrade then you won’t be able to use the previous version of Gramps, even if you subsequently backup or export your upgraded Family Tree.
You can still use the previous version of Gramps – just not with the upgraded tree. So the message could intimidate users with multiple trees that need to be converted.
Our dialogs use the standard icons: “dialog-question”, “dialog-error”, “dialog-warning” and “dialog-information”. They are common to an icon theme, not an OS.
Try changing an icon theme whilst the dialog is open. The icon changes as expected.
It looks like Windows is displaying the Adwaita icon with a bad scaling.