For ODB2, I simply got a bluetooth adapter which plugs onto the ODB2 connector in the vehicle. My smartphone then pairs with that, and I run Torque Lite to see all kinds of neat stuff.

The one I got was a generic $20 thingie off eBay years ago, but pretty much any/all of them will work --> they're just serial-to-bluetooth adapters really. Apparently "elm 327" is what is inside the one I have.

Eg. https://www.amazon.ca/KITBEST-Scanner-Bluetooth-Diagnostic-Adapter/dp/B01BY2CK32/

EDIT: Oh, that's for Android. Dunno about for iStuff.

Here's the iOS version from the same brand, using WiFi instead of Bluetooth:
https://www.amazon.ca/Diagnostic-Professional-Supports-Compatible-Vehicles/dp/B01BY2CLMC/ (also works with Android).