I had one plus 8 pro brand new phone Android 10. I sold the phone in a week's time. I never set any password or screen lock. I understand android 10 uses file-based encryption. I just did a factory reset and sold the phone. can the buyer retrieve by data though I have not set the screen password? will the file-based encryption take care?
The file encryption on Android 10 is used no matter if you have set a lock screen password or not. The file encryption does incorporate the password but an additional secret random key is also required for accessing encrypted files.
This key is erased on factory reset, so encrypted files become impossible to decrypt.