Missing Files After Ransomware Cleanup?

I personally faced a situation involving ransomware, and the affected systems have since been cleaned and reimaged. Although most data was recovered using the backup system, it is apparent that some critical data is missing and could have been deleted as a result of the attack.

In those circumstances, what are the best ways available for restoration of leftover/partially lost data from the affected drives?

Are there ways to scan storage devices for data that didn’t come back via backup? Finding ways of recovery that works!

any help would be appreciated.