You could look into AWS Glacier or S3 Deep Storage tier. If you have 20TB stored that’s about $20/month(YMMV) which isn’t wonderful but that’s a lot of data so it’s understandable.
Being a cheapskate, if I can get something back or it’s not crucial it’s on a RAID array with snapshots, everything else is either encrypted Duplicati backups to Google Drive (Windows) or encrypted borg backups to Borgbase(Linux)
Borgbase is very reasonably priced and if you have a large storage space in GDrive due to having one of their other services it’s a good use of it.
It would be marginally risky, but considering how many people have large storage arrays having a “mutual backup compact” between two folks where each can run backups to the others array would help get you an affordable offsite backup for catastrophes.
I see a bunch of people with 10TB of data and 30TB arrays and if two of them got together they would both be reasonably safe from a total array failure.