As of now there are not AAAA records for the S3 endpoints nor for the (optional) CDN:
$ dig <bucket>.ams3.cdn.digitaloceanspaces.com AAAA +short => cds.b5g9b8e4.hwcdn.net.
$ dig cds.b5g9b8e4.hwcdn.net. => NOERROR but not AAAA records
In 2019 it should be state of the art to deploy services with IPv6.
I am running a few IPv6-only services and being able to access my bucket is critical for making any kind of use out of the DO spaces offering... I feel a bit tricked. Neither the website nor this "forum" provide IPv6 as well...