Also, I'm trying to figure out a way to use AWS S3 Deep archive to backup my data.

Restic can automatically dedup by chopping files into chunks and it support S3. However, it doesn't support deep archive tier.

I have implemented the chunking parts, but not sure how I'm going to recover the archived files. Like what operations need user to do, what parameter is needed. I'm targeting AWS S3 specifically, so no need to worry about other backends.