There are no mic preamps or ADCs for recording from external devices in smartphones, unless it's an older phone with a TRRS jack which would accept a mono analog mic input on a set of wired earbuds. The mic preamps and converters for what is being discussed here will be in the external interface you connect.
I believe you are wrong.
Admittedly my experience is only with iPhones - but the Lightning or USB-C input can easily be adapted to 3.5mm TRRS input with a simple converter and used with a mic/headset, headphones etc. It seems this is what OP and others are talking about when mentioning a "3.5 to usb-c adapter" in his first post.
(i imagine similar to this:
https://www.apple.com/shop/product/MW2Q3AM/A/usb-c-to-35-mm-headphone-jack-adapter)
It has no preamp or audio interface build in. It is intended for a headset with mic to use for taking calls and substitutes the old trrs input. But you can connect a microphone directly to that with a TRRS to TRS adapter so there must be a build in converter/preamp (and PIP) in the smartphone - how else would it work?
I have recorded countless times in mono this way with a lav mic.
If you want to record stereo you need an audio interface (like Røde AI-Micro, or that which is build into an MV88 etc.)