Are internal memory deleted temp files saved in a backup?

[AC Question]

I would like to root my LG G4 H812 in an attempt to recover some photos. It runs marshmallow 6.0 so I would need to downgrade in order to root. I plan to do the one that doesn't require unlocking the bootloader. Once I flash an older version, my data to recover will likely be wiped, I'm assuming. Are those potentially recoverable files saved when I do a backup, and can the phone be restored with all those deleted files I want to search through? TIA, from a root newbie.

 

[ManiacJoe]

Once I flash an older version, my data to recover will likely be wiped, I'm assuming.

Most likely. When files are deleted, the space they used to use is marked as "free for use". Any writes to the storage after the deletion can overwrite the data you want to recover.

Are those potentially recoverable files saved when I do a backup, and can the phone be restored with all those deleted files I want to search through? TIA, from a root newbie.

Any backups will contain only the non-deleted files.
Older backups may still contain your now-deleted files as long as the files existed at the time of the old backup.