I managed to install tcpdump on the Asus RT-AX82U with Singtel TV box connected.
Here are some snipts of the capture. Looks like IGMP is there and there are only VLAN 20 tagged traffic to the TV box. 10.247.96.197 is the IP address of the Singtel TV box.
Ethernet MAC address range 01:00:5e:xx:xx:xx is for IPv4 multicast packets.
/tmp/home/root# tcpdump -vvnne 'host 10.247.96.197 or (vlan and host 10.247.96.197)'
tcpdump: WARNING: archer: no IPv4 address assigned
tcpdump: listening on archer, link-type EN10MB (Ethernet), capture size 65535 bytes
16:38:30.338570 TV Box Mac address > 01:00:5e:48:0a:**, ethertype 802.1Q (0x8100), length 64: vlan 20, p 4, ethertype IPv4, (tos 0x58, ttl 1, id 9348, offset 0, flags [none], proto IGMP (2), length 32, options (RA))
10.247.96.197 > 239.200.10.203: igmp v2 report 239.200.10.203
16:38:31.556149 TV Box Mac address > 01:00:5e:7f:ff:fa, ethertype 802.1Q (0x8100), length 459: vlan 20, p 4, ethertype IPv4, (tos 0x58, ttl 1, id 9349, offset 0, flags [none], proto UDP (17), length 441)
10.247.96.197.1060 > 239.255.255.250.8082: [udp sum ok] UDP, length 413
16:38:34.557113 TV Box Mac address > 01:00:5e:7f:ff:fa, ethertype 802.1Q (0x8100), length 459: vlan 20, p 4, ethertype IPv4, (tos 0x58, ttl 1, id 9350, offset 0, flags [none], proto UDP (17), length 441)
10.247.96.197.1060 > 239.255.255.250.8082: [udp sum ok] UDP, length 413
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