The whole framework of secular versus religious government does not actually work very well when we are talking about Islam.
This is an adopted contrast taken from the specific experience of Christians in Europe, where the pope was basically an emperor, or the king was also the head of the church; and religious leaders were considered divine. That is pure theocracy. We don’t have that concept in Islam. But since we have adopted this framework, it has caused us a lot of confusion, and can breed extremism.
The truth is, we have always integrated man-made legislation into our jurisprudence. Any Islamic government would have to, because, frankly, the Shari’ah does not deal with the overwhelming majority of things governments have to deal with.
I shudder to think what a state would actually look like if literally the ONLY law they had was Shari’ah, without any man-made legislation; if everything that is unaddressed by the Qur’an and Sunnah was just left unregulated in any way. No ruler or scholar of the past, including the Khulafah Rashideen thought it should be this way. This is why we have things like ta’zir (judicial discretion) and ‘urf (customary practices) as sources for rulings.
We never had to choose between religion and state, because they were never mutually exclusive in Islam. We always had Shari’ah and we always had Qanoon.
It is a modern development in the Islamist movement to pretend that there can only be Shari’ah, and man-made rulings are kufr. Anyone who lived during any period of Islamic history would have found that concept to be laughable.