A long time ago when I was playing with rolling my own PKI, each of Android, iOS, Chrome, Firefox, and even Internet Explorer allowed me to install a root CA by opening the .crt file. From what I remember, iOS popped up some warnings and added the cert as part of a profile, but it did work.

I know things like MDM/Intune/Group Policy/etc and such can A) faciliate doing this on a large number of devices and B) prevent users from doing this on their own.

Does this not work anymore?