Ipad mini 1 as HomeKit hub

Since they say you need the latest version of iOS that would be iOS 12 or higher. But in researching Homekit, it was released with limited functionality in iOS 8. If you have more modern Homekit devices you want to control, that is why Apple is likely saying you would need iOS 12, which requires a very modern device. iPad Mini first generation is only capable of running iOS 9.3.5.

Nope, it won't work. You need a more modern device with the latest version of iOS, which an iPad Mini 1st generation cannot be upgraded to.

See this link: https://support.apple.com/en-us/HT204893