The “Save” button uses the accent color which is blue by default. With configurable accent colors coming to GNOME 47 and GTK/Libadwaita, you can choose a red accent color.
See the original description of the screenshot:
It’s now using standard button styles, fixing the long-standing issue where suggested and destructive buttons would look the same when using red accent color
I have no idea when I last updated my RasPi 0s (none of which is exposed to the public).