Use IPv6 addresses only when resolving hostnames, and not for example try IPv4
So you now your isp is to blame. You probably only get an ipv6 address on your home router, and somewhere all the traffic is gathered from many users and pushed through a common gateway to connect with the ipv4 internet. It works…but can lead to problems if not configured correctly. Like getting automatic captchas not working, or being banned from sites you never visited, or suddenly being logged out. In my case (part of the Vodafone network in Germany), it was exactly like in your case - a couple of sites did not want to open. Everything else was ok, the sites were fine with vpn or other isp. And they did not fixed it for months.
So try the curl with -4 and -6 from your mobile (like making a hotspot from the cell phone) and if it works you know who to blame.
p.s. i tested - works on both protocols, so it is issue on your side - isp, router, pc config…