Azure Backup - On premise server: Finding the last untanined version of file

Question

We have an app that uses a sql db and onto disks stores millions of files. These files are pdf documents.

if ransomware attacked a vm, how to find the correct untained version of the file for every single one of those million files?

I've tried the procedure of recovery from a backup. I can choose a day back in the history and mount drive for this day. But do it million times?

I am asking because I am considering another way and I need a comparison.
The other way is to write a small app that will incrementally use azcopy to a Azure Blob Storage with immutable option switched on.

Jan