DNS over TLS

I have set up Cleanbrowsing DNS on my Fritzbox 7530 router. With other DNS providers (Cloudflare/Google/Quad9) when I enter the DNS resolver four DNS addresses (2 IPv4 and 2 IPv6) appear in the list of DNS servers used, but with Cleanbrowsing there is only one IPv4 address (185.228.168.9). Is this setup correctly? My main concern is the lack of any IPv6 address.
Also, what is the correct URL for DNS over https in Chrome as the one given on the page below does not seem to work: https://cleanbrowsing.org/guides/dnsoverhttps
Finally, I have set up Cleanbrowsing on my Android phone and tablet using the private DNS setting (DNS over TLS) and when I test IPv6 using https://test-ipv6.com/ I get 9/10 and it says that ‘Your DNS server appears to have no access to the IPv6 internet’. This does not happen with Cloudflare/Google/Quad9, and I think that it is related to my first question about the lack of an IPv6 address.