The wiki says what you tried is not yet implemented: You have to obtain the handle to delete a rule. The example is:

$ sudo nft -a list table filter
table ip filter {
      ...
      chain output {
            type filter hook output priority 0;
            ip daddr 192.168.1.1 counter packets 1 bytes 84 # handle 5
      }
}

The -a shows the assigned handle "5" as a comment, so you can

$ sudo nft delete rule filter output handle 5

The wiki says what you tried is not yet implemented: You have to obtain the handle to delete a rule. The example is:

$ sudo nft -a list table inet filter
table inet filter {
      ...
      chain output {
            type filter hook output priority 0;
            ip daddr 192.168.1.1 counter packets 1 bytes 84 # handle 5
      }
}

The -a shows the assigned handle "5" as a comment, so you can

$ sudo nft delete rule filter output handle 5