Determining unique source/destination IP addresses separately.

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Statistics -> IPv4 Statistics -> Source and Destination Addresses
Statistics -> IPv6 Statistics -> Source and Destination Addresses

The menu items above look like a gui front end to the tshark options:

-z ip_srcdst,tree[,filter]
Calculate statistics on IPv4 addresses, with source and destination addresses separated into separate categories.

-z ip6_srcdst,tree[,filter]
Calculate statistics on IPv6 addresses, with source and destination addresses separated into separate categories.

(The output is suspect. A test capture with IPv4 and IPv6 packets, IPv6 addresses appear in the IPv4 statistics.)

This can be done with tshark pulling the ip.src and ip.dst fields and crunching the output.
Be aware that some packets (e.g. ICMP and ICMPv6) include an extra IP header so there are multiple ip.src and ip.dst in the packets.

$ tshark -r ./*10130* -T fields -e ip.src | sort | uniq | sort -n | wc
    176     175    2840
$ tshark -r ./*10130* -T fields -e ipv6.src | sort | uniq | sort -n | wc
    178     177    5412

Lower counts when only counting the first occurrence of the field in each frame.

$ tshark -r ./*10130* -T fields -E occurrence=f -e ip.src | sort | uniq | sort -n | wc
    169     168    2474
$ tshark -r ./*10130* -T fields -E occurrence=f -e ipv6.src | sort | uniq | sort -n | wc
    176     175    4502