a device does not have a SDK level, a device runs an Android version, and it looks like you are trying to say, your device is running Android 10...
App Inventor currently targets SDK 29 an will very soon target SDK30... this is independant on the Android version your device is running... and this upgrade will change a lot especially regarding storing files... I hope, that we then will be able to store a text file in a shared directory again, but as you have seen in the discussion with @Anke, I might be wrong...
as a temporary workaround you can use the file extension App Inventor Extensions: File | Pura Vida Apps and copy the file from the ASD to the destination directory... however this will stop working after App Inventor targets SDK30...
Taifun