First, if you rooted with Magisk, you can unroot completely. If you used a system root, yes or no to the unrooting completely. If all the rooting process did was put su into /system/xbin, sure, just delete the file. If it did other things that you weren't aware of, and some apps looked for them to determine rooting, no. And if you sent the phone to Samsung for repair, the mere presence of DiskDigger on the phone might cause them to void the warranty. (I had a recent go-around with Google over a problem with the Pixel 2. I sent them a debug dump and they advised me that there were apps on the phone that required root, so I'd have to flash a stock ROM first, then redo the actions and produce the dump.)
Read the responses - many apps like this (undelete apps) get a review stating that it's garbage because it doesn't recover anything, not mentioning that it wasn't looking for deleted files, it was trying to recover files after a factory reset, which is a different thing altogether. DD looks in the directory for files marked "deleted", then flips that bit and rebuilds the list of blocks used by the file. A FR rebuilds the directory leaving no sign of the files that used to be on it.
Or it's a complaint that all it was able to recover was .jpg files. Read the description. That's all the free version will recover.
Or it recovered files that were useless. Once a file is marked deleted, other writes to storage can write over the places those files occupied. When you "recover" those files, you're recovering a piece of the file, a piece of another file that wrote into that unused space, another piece of the file, etc. Once anything writes to storage (and that includes every single app that runs - stuff you tell to run, stuff that just runs because Android is running, stuff that Linux runs (the operating system that Android runs in is Linux) - any write - pieces of a file you're trying to recover can be overwritten, and there's no longer any way of recovering them. A backup is always the best way of recovering a deleted file, you copy it from the backup.
Even rooting and installing DD can overwrite some files you're trying to recover. At very least, even if each file you're installing is one sector in size, you're installing the Magisk binary, the Magisk manager and DD. (And you're probably going to have to install TWRP to install Magisk. If the phone is AT&T or Verizon, you can't even do that.
And I just re-read your first post. You did a factory reset. So you can root the phone if you like - I always have TWRP and root on a phone. At the very least, just before doing an update (and with a Pixel, that means every month), I do a TWRP backup and copy it, and any changes I've made in the "internal SD card" to my PC as a safety measure. (And that means that the easiest way of doing the update is doing a Deuces factory OEM flash without wipe. Otherwise I have to somehow uninstall TWRP, restore the boot.img file, update, redo the change that Magisk makes to the boot.img file, reinstall TWRP - Deuces is a lot easier and faster. Even including the Magisk modules I have to reinstall.)
But ... having done the FR, there are no more deleted files listed in your directories in most phones. (I've never owned any variant of the S7, so I can't say.) That would mean nothing recoverable. From an external SD card? Yes. There's a program called PhotoRec that can recover the
files - it doesn't look at the file
system (like the directories). But there's no version for Android, so you'd have to use dd (which you'd probably have to get from BusyBox, which you'd have to install after you rooted) to make an image of the userdata partition, then mount that file as a drive in your PC, then use PhotoRec on that. And if you're not familiar with Linux, you will be after using PhotoRec.
As for Ubuntu on your PC, no. All the PC sees is what the phone sends it via the USB port - which is
non-deleted file names. Ubuntu can't look in the directories in the partition in the phone, so good idea but it won't work.
But that's moot, since you did the factory reset. See if, in that article, you can install TWRP to
your variant of the S7. At least making backups will be easier. Then make one once a month. Or just back up every app (
Apk Extractor will do that), every picture, every music file - everything you don't want to lose. Then, if you ever do a factory reset again, all you'll lose is half a day or so, plus anything since the last backup.
Undelete apps are nice (if I'm correct, I wrote the very first one, for CP/M, in 1973. I've never heard f an earlier one. So of course I like them.) But nothing can bet an off-site backup. If the house burns down, taking your phone and PC with it, your insurance will buy you a new phone and a new PC - but it won't buy you replacement data. Your backup in the cloud will do that - for free.
(Any spelling errors or typos are strictly mine and unintentional.
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