What is the ruling on judging by other than what Allah has revealed, and what is the ruling on mixing (of sexes) in all its forms?

Whoever rules by other than what Allah has revealed, believing that it is better than Allah's rule, commits a major disbelief (kufr akbar) that expels him from the fold of Islam. However, if he rules by other than Allah's rule out of desire or caprice, then it is a minor disbelief (kufr asghar), a disobedience, and a great sin. Allah's Sharia must be the governing law, and to it, people must refer. Al-Shanqiti clarified that associating partners with Allah in His judgment is like associating partners with Him in His worship, and that what Allah has made lawful is lawful, and what He has forbidden is forbidden, and the religion is what Allah has legislated. Thus, any legislation from other than Him is false, and acting upon it instead of Allah's legislation, by whoever believes it is equal to or better than His, is a clear disbelief (kufr bawāḥ). The Quran indicates that there is no judgment except for Allah, and that following legislation other than His is disbelief in Him.