Actually I followed the instructions in this YouTube video:
- in: 'Settings - General - Developer options - Select USB Configuration' changed fro MTP
- used adb shell command "sm partition disk [disk id] mixed 20
" instead of "sm partition disk [disk id] private
- renamed just now created "internal storage"
from "SD card
" to "SD card as internal storage
", so it can be distinguished from the real SD card.
From now on installed apps can be removed from Internal storage to "SD Card as internal storage": 'Setting - General - Apps - select desired app - tap on Storage - Change - select "SD Card as internal storage" - Move'.