I want to split one MicroSD card into two parts: part adoptable storage, and part normal storage. How can I do this? I don't want all my storage as adopted storage, so I was wondering how I can split it into 1 part adopted storage and 1 part normal file storage (what Android calls "portable storage").
You don't need to root your device but the device i done this with is rooted


You need to enabled Developer Options.
Enable the USB Debugging option.
Make sure your SD card is formatted as portable, then get the adb executable (see our adb tag-wiki for details).
Connect your device to your PC and run the adb devices command. If your device is connected correctly you will see your device listed in the output.
Run adb shell sm list-disks adoptable. This will show you the list of disks that can be used for what we want.
For my device it showed me disk:179,128 so i ran adb shell sm partition disk:179,128 mixed 80 on my 32 GB AS card. It gave me 5 GB as adoptable storage and the rest for other uses. (This will format your SD card.)