In a few exchanges with tech support reps for Teclast and Chuwi, I learned that they use Kingston uSD (aka TF) cards to test their claims for uSD compliance, and they also know that some brands don’t work if not formatted in the device itself (and even then, non-Kingston SDXC cards may not work). So, if all else fails, try Kingston uSD.
https://en.wikipedia.org/wiki/Secure_Digital#SDXC