IPv6 not working on Debian 11 with nftables/nginx

I'm running a webserver (nginx 1.21.6) on a Debian 11 system with nftables 0.9.8. My nftables configuration is:

table inet filter {
chain input {
  type filter hook input priority filter; policy drop;
            ip saddr @spamhaus4 counter packets 0 bytes 0 drop
            ip6 saddr @spamhaus6 counter packets 0 bytes 0 drop
            meta l4proto tcp meta nfproto ipv4 ip saddr @abused counter packets 0 bytes 0 drop
            ip daddr 46.38.148.0-46.38.151.255 drop
            iif "lo" log group 2 accept
            iif != "lo" ip daddr 127.0.0.0/8 counter packets 0 bytes 0 drop comment "drop connections to loopback not coming from loopback"
            iif != "lo" ip6 daddr ::1 counter packets 0 bytes 0 drop comment "drop connections to loopback not coming from loopback"
            ct state established,related log group 2 accept
            ct state invalid counter packets 47 bytes 2572 drop
            tcp dport { 25, 80, 143, 443, 587, 2772, 9980, 45907 } log group 2 accept
            ip protocol icmp icmp type { echo-reply, destination-unreachable, echo-request, router-advertisement, router-solicitation, time-exceeded, parameter-problem } log group 2 accept
            ip6 nexthdr ipv6-icmp icmpv6 type { destination-unreachable, packet-too-big, time-exceeded, parameter-problem, echo-request, echo-reply, nd-router-solicit, nd-router-advert, nd-neighbor-solicit, nd-neighbor-advert, ind-neighbor-solicit, ind-neighbor-advert } log group 2 accept
            ip6 nexthdr ipv6-icmp log group 2 accept
            counter packets 2686 bytes 421604 drop
    }

    chain IPSinput {
            type filter hook input priority filter + 10; policy drop;
            counter packets 88448 bytes 15799025 queue num 0-3 bypass,fanout
    }

    chain forward {
            type filter hook forward priority filter; policy drop;
    }

    chain output {
            type filter hook output priority filter; policy accept;
    }

    chain IPSoutput {
            type filter hook output priority filter + 10; policy drop;
            counter packets 76196 bytes 201278628 queue num 0-3 bypass,fanout
    }
   }

The nftables firewall works fine.

However, my nginx server(s) are not reachable via IPv6. I have used different IPv6 checking tools (e.g., https://ipv6-test.com/validate.php) and also Qualys ssltest cannot access the server via IPv6, IPv4 is working fine however. I have included the listen [::]:80;(resp. listen [::]:443;directive in each of my nginx servers. And netstat -anlp |grep nginx gives

tcp        0      0 0.0.0.0:80              0.0.0.0:*               LISTEN      48846/nginx: master
tcp        0      0 0.0.0.0:443             0.0.0.0:*               LISTEN      48846/nginx: master
tcp        0      0 192.168.42.98:443       93.104.163.178:39001    VERBUNDEN   48847/nginx: worker
tcp        0      0 192.168.42.98:443       93.104.163.178:39368    VERBUNDEN   48847/nginx: worker
tcp        0      0 192.168.42.98:443       93.104.163.178:43086    VERBUNDEN   48847/nginx: worker
tcp6       0      0 :::80                   :::*                    LISTEN      48846/nginx: master
tcp6       0      0 :::443                  :::*                    LISTEN      48846/nginx: master
unix  3      [ ]         STREAM     VERBUNDEN     160451   48846/nginx: master
unix  3      [ ]         STREAM     VERBUNDEN     160453   48846/nginx: master
unix  3      [ ]         STREAM     VERBUNDEN     160450   48846/nginx: master
unix  3      [ ]         STREAM     VERBUNDEN     160448   48846/nginx: master
unix  3      [ ]         STREAM     VERBUNDEN     160452   48846/nginx: master
unix  3      [ ]         STREAM     VERBUNDEN     160446   48846/nginx: master
unix  3      [ ]         STREAM     VERBUNDEN     160449   48846/nginx: master

On my router, I have activated IPv6 too.

Do anyone have any ideas where the issue could be?