Yup this is why these vendors exist. You’re definitely not alone, cloud repatriation is a ‘thing’.
These vendors have replaced that Ceph or Minio expert others in this thread said you’d need to budget for, by software. The system detects dead/degrading disks and automatically evicts them and rebuilds that chunk of the erasure code on another disk. Every few months you go in and hot swap the bad disks = the ones with a blinking led. Also Prometheus metrics, alerts in case of issues,... You don’t need a storage admin babysitting this.
1 rack of 4u90 enclosures with 18TB disks is 15PB RAW so with erasure coding overhead about the 10PB usable you need today.
I’m obviously biased on which vendor to pick. Do your due diligence, f.i. on how the system does capacity expansions.
It probably depends on if you are tied at the hip to other AWS services. If you are, then you're kind of stuck. The ingress/egress traffic will kill you doing anything with that data anywhere else.
If you aren't, the major players for on-prem S3 (assuming you want to continue access the data that way) would be (in no specific order):
Cloudian
Scality
NetApp Storagegrid
Hitachi Vantara HCP
Dell/EMC ECS
There are plusses and minuses to all of them. At that capacity I would honestly avoid a roll-your-own unless you're on a shoestring budget. Any of the above will be cheaper than Amazon.