You have not mentioned Android 12 in this Topic, you wrote it as "android version in phone is 12" - so my search of the page did not find the info -oh the wonders of the internet. 
Android 12/13 have the most strict security measures and they affect file handling among other things. Here is an overview by Power User Anke that you need to study:
Although you have requested write permission:
- Should be done from Screen1 to give the whole App permission
- The folders/directories you can use remain limited