Hello,
I wanted to report that I've been encountering the same issue as the user who submitted a bug regarding Safari's Developer Tools. Like them, when I attempt to uncheck a style property under the 'Elements' section, the entire element's CSS gets removed, and sometimes even the entire webpage's CSS. To provide further clarity, I've attached a video in MOV format demonstrating this issue.
I want to emphasize that I've ensured all my software is up to date, and this problem has been persisting for a minimum of four months.
Thank you for your attention to this matter.
Best regards,
Lukáš
Video on YT
https://youtu.be/oGszww9boiA