The internal implementation of the Toolbutton style has changed on macOS since Mojave was released - Marc Culler has done a lot of work to update the Aqua theme, make it compatible with Dark Mode, and bring the buttons visually in line with how Apple's apps render them (NSButton vs. the HITheme API that Tk uses). Pic #1 is the new, modern style--the slightly rounded buttons. Pic #2 is the old, flat style of Toolbutton. Your presentation of these images is slightly confusing. If you prefer the rounded style, then great, that is what is now being supported. If you prefer the older, flatter style, I'm sorry - I don't see a case for rolling back Tk to support that style of button as it is more or less visually obsolete on Mac.