I find the current magnet strength more than enough - why do you think they need more? I use my 12 Pro in an Apple leather MagSafe case with a third-party magnetic mount in my car and it's rock solid.
I use third party clear cases generally - don't like the ring on Apple's clear case - and I'm thinking of getting the Belkin 3-in-1 charging stand, hence wanted stronger magnets due to the third party case.....