I tried to format SD card as internal storage. But every time I tried, it corrupted the SD card. It would complaint about SD card is too slow. But I have sdhc class 10. I can format it on my PC. It will be fine. When I put it in my new G 4 phone, it is happy with the card. But when I tried to format it on my phone, the same thing happened.
A Class 10 MicroSD card should indeed work. That said, if your phone won’t format as adoptable storage, your best bet is probably to try another brand of MicroSD card. In case it helps, Motorola’s guidance is here: Using an SD card - Moto G (4th Gen.).