HomePod Mini keeps joining my iPhones network when I only want it on my IoT network

I want my HomePod Minis to be set up on my IoT network to prevent devices from accessing my computers, data storage, etc... This is a standard best practice for any network. My HomePod Mini keeps joining my iPhones network when I only want it on my IoT network, the minis control other homekit devices (schlage locks, Wemo Doorbell, etc....) that I absolutely do not want accessing my main network. Is there a way to force my minis onto the IoT network and restrict them from my main network while allowing my iPhone to be on the home network and only join the IoT network from time to time?

This seems like something Apple should definitely fix.

Thanks!