I have a Macbook Pro. What kind of USB hub/dongle/adapter should I use to operate the miHealth or Bluetooth Scanner?

You will need an adapter that goes from USB-C to USB. There are many versions available, while we do not have a specific recommendation for which adapter to use, we know that at this time OTG adapters do not work.

OTG which stands for On-The-Go is a specification that allows tablets or phones to act as a host allowing other USB devices to be attached. For example, connecting a USB keyboard to a phone.
More information here:
https://www.coolblue.nl/en/advice/what-is-usb-otg.html
https://en.wikipedia.org/wiki/USB_On-The-Go

The miHealth does not support this OTG specification. While we cannot test every adapter, here is one that we have found to work.
https://www.amazon.com/Syntech-Adapter-Compatible-MacBook-Thunderbolt/dp/B09H2TJCQG

Please ensure that your device is listed as one of the supported models in the item description. You could try any other USB C to USB Adapter, specifically USB C Male to USB3 Female Adapter as long as it's not OTG.