Ustadh, Ihsan Allahu Ilayk, at the end of Thalathah Usul we discussed ruling by other than Allah's rule. I read further and the Shaykh talked about istibdal. Is my understanding correct that istihlal is also taken into consideration for this?

Sometimes the scholars speak in general terms that need further explanation and they themselves explain them at other places and give the necessary details. I went in length and quoted imam ibn uthaymeen on this in my known series on youtube replying crystal clear to the people of takfeer.