Multicast TV firewall rule without conntrack?

I have a question regarding igmpproxy multicast tv. As far as I see, the connection used for the udp stream never gets into ESTABLISHED status. I believe this is as there is no packet returning the path so conntrack is not realizing it.
But as multicast tv is quite often used in Germany and Switzland, I wonder if there is a conntrack helper to fix it.

The rules created by igmpproxy is in the zone_kodi_dest_ACCEPT which is behind all filter and traffic rules. As the connection is not going into established status, every of those packets go through the full packet filtering ... am I right? As tv is a huge amount of packets I would assume that establishing such connection would reduce load on the router.

This is my igmpproxy configuration:

root@home:/etc/config# cat igmpproxy
config igmpproxy
    option quickleave 1
#    option verbose [0-3](none, minimal[default], more, maximum)

config phyint
    option network wan
    option zone wan
    option direction upstream
    list altnet

config phyint
    option network kodi
    option zone kodi
    option direction downstream

[pictures to be added later]

I solved the problem for me by adding an extry rule to the Firewall Custom Rules Set:

iptables -I FORWARD 4 - i wan -o kodi -p udp -d -j FLOWOFFLOAD

This is a duplicate to the rule created by igmpproxy but with FLOWOFFLOAD. Now the udp stream is offloaded even if offload is not used in general (due to problems in 21.02).

I suggest to add the FLOWOFFLOAD to the igmpproxy package (but don't know how to).