Uhm, they did: https://support.apple.com/en-us/111857
It was compatible with all MagSafe iPhones, but was sized for the mini and was most useful with it in terms of capacity boost. I still use it occasionally.
I missed that, probably because I bought the mini fairly late 2022, it will be 3 in 2025/12 🎉
I appreciate however the Wallet that I bought with it.
It would be difficult to have both the Wallet and the Magsafe Battery, at least simultaneously.
I’m doing fine with a Power bank, that gives the mini the extra juice at times.