Turns out that the issue can be overcame by passing a -o bucket_size=64PB option on the s3fs mounting command. See S3FS repo issue for more details: Can one increase the reported available space on mount? · Issue #2489 · s3fs-fuse/s3fs-fuse · GitHub
I think we can close this issue and hope that others will find useful. It would also be awesome if the Deja-dup devs keep in mind users who utilise s3fs integrations as a replacement of the legacy AWS S3 storage option. Though I appreciate it’s no longer officially supported, it’s an integration currently used by many users.
Thanks for the work you put on this.