It's MacOS, or at least I know MacOS does that.
One solution would be to run a local DNS service like Cloudflare DNS-over-HTTPS proxy and then enter ::1 (IPv6 loopback) as your DNS. I bet that would work, but I haven't tried it. It also improves privacy and security on untrusted networks. Not sure how it handles the captive portal problem though. Maybe Cloudflare's service has a shim for that.
MacOS used to do the simple thing, but at some point in a recent release they started being "smart" and added this annoying restriction.
The problem I ran into with ipv6 is that the OS (either macOS or Android, I don't recall which unfortunately) won't query for AAAA records when it does DNS lookups unless there is a DNS resolver configured that is reachable over ipv6.
ZeroTier doesn't provide its own DNS, so I'd manually entered A and AAAA records into Google Cloud DNS on a domain I own, but because of that quirk I wasn't able to use ipv6 since my Internet links at home and work were both ipv4 only.