~As far as I know, bucket names are public via certificate transparency logs.~ There are tools for collecting those names. Besides you'd leak the subdomain to (typically) unencrypted DNS when you do a lookup and maybe via SNI.

Edit: crossout incorrect info

I just started using hashes for names. The deployment tooling knows the "real" name. The actual deployment hash registers a salt+hash of that name to produce a pseudo-random string name.

This is all good and we'll on the IaC side,yes. But at the end of the day, buckets are also user facing resources, and nobody likes random directory / bucket names.