I too have the
Mavic 2 Pro and purchased the iPad Mini 5 specifically to use it as a controller. Yes, it will "fit" into the controller arms, but you have to really force it in, and there is considerable outward pressure on the arms because you are going to be forcing them slightly beyond their normal fully opened position.
There are quite a few mounts you can buy which will mount any tablet, including the Mini, but almost all of them mount the tablet
above the controller. I didn't like having to give up my controller display because I find it easier to read some of the basic information on the controller display rather than on iPad DJI Go app, but more importantly, I find it useful to be able to see the buttons and not have to fumble around for them.
I designed my own mount and printed it on my 3D printer (I've posted this before):
Mavic 2 Pro iPad Mini 5 Mount
I realize that this is not an option for most people reading this, but I post it merely to show that it is possible to mount the pad
below the controller. I think I did see at least one commercial design that mounted below, by attaching to the body rather than to the arms themselves, as I did. I don't have that link handy, but if you just do a little searching in Google you'll find it. A search on Amazon will quickly turn up over a half dozen above-controller mounts.