Yes. This. I tried using ipv6 and had to turn it off because of problems like this.
And this is well known in the industry. The IPv4 world has had enormous mapping and trust ratings and understanding -- coupled with a scarcity that gives range owners or operators a higher incentive to care about what happens on it -- while a lot of people are still completely in the dark about IPv6 and still treat it like some scary unknown.
Indeed, and residential ranges are wholesale blocked from participating in various services, because of abuse through compromised hosts in residential networks.
Budget cloud providers are wholesale blocked from participating in various services, either at thier local edge, or the remote edge, because of abuse through deliberate malicous customers and/or compromised hosts.
I have Google Fiber, and I can't say I get a ton of captchas (other than sites that have them for everyone, e.g. unauthenticated contact forms). The only downside to v6 was I had to get a new router because my old one couldn't route v6 at gigabit speeds (could easily do gigabit symmetric on v4 only, but topped out at 400/400 Mbps on dual-stack).
Back when I had Spectrum (which was Charter in my area pre-merger), their v6 worked fine as well.