Android 9 (Pie) sd external card conventions My Moto g6 asked to reformat my SD card after the official Pie update. No app was able to access the SD card and only the System and Total Commander even recognized it. After Android formated, I could read from and write to my SD card. The problem is the following. 

I fast transfer my libraries from my computer. This is I put the card in my computers card reader and copy my files into the root of card's directory tree. (I don't see that it matters but I rsync from a Linux installation.) Now android wants to reformat again as if I hadn't formatted. To restate, no app is able to access the card and only the System and Total Commander recognize it.

Where should I move the files, and where can we check the conventions? What are the protocols and what is going on with Pie? Any references are welcome as well as a direct answer, thank you.

Possibly related question: SD card is unwillingly used for apps
The card was corrupted at removal time because it wasn't properly ejected (unmounted) beforehand. Remember to eject your removable devices even if you think it is safe to remove them.