What program is better to recover files for a beginner in this matter?

Question

Data recovery

Hello!
The bottom line is this: the OS was reinstalled, the disks were merged into one, then divided into 2. One has a new OS, the other is empty. The second disk is not formatted.
1) Why do some programs require you to format the disk, others don't care?
2) What is the best program to recover files for a beginner in this matter?
Thank you.

Answer 1

cm . https://www.piriform.com/recuva what it finds, it will show,
but if the format is here xs, you need to look into something low-level, but there are few chances