I have both the Apple leather case and the Apple clear case for my new iPhone 12 Pro. I just tried gauging the relative strengths of the magnets on the charger and my Apple MagSafe wallet.
For me, the magnets were nearly the same in terms of pull strength so attachment to the wallet using either the clear or leather case was good. However, one significant difference was the degree to which the wallet would move once attached to the respective cases. With the leather case, since the finish is leather and has a bit of texture, once the magnets on the wallet stick, the combination of stiction and magnet pull keeps the wallet in place fairly securely. In contrast, with the clear case, since it is so smooth and devoid of texture, there is far less stiction and the wallet is easier to move on the case. I think this would be an issue, since it would be possible to more easily have the wallet move inadvertently or accidentally, and it could more easily pop off the magnets.
I think if you are concerned about a secure connection between a case and the wallet, the leather might be the better choice for you.
Hope this helps.