Comment 14 for bug 2049220

I have manually downloaded and installed the updated package and can confirm the new package contains the correct firmware and the issue is resolved now. IPv6 Multicast is working and IPv6 address autoconfiguration is working as expected.

Some output:

fludizz@pauwel:~$ dpkg --list | grep linux-firmware
ii linux-firmware 20220329.git681281e4-0ubuntu3.28 all Firmware for Linux kernel drivers

fludizz@pauwel:~$ sudo dmesg | grep mt7921e
[ 8.912585] mt7921e 0000:05:00.0: enabling device (0000 -> 0002)
[ 8.918209] mt7921e 0000:05:00.0: ASIC revision: 79610010
[ 9.000053] mt7921e 0000:05:00.0: HW/SW Version: 0x8a108a10, Build Time: 20231109190918a
[ 9.012216] mt7921e 0000:05:00.0: WM Firmware Version: ____010000, Build Time: 20231109190959
[ 9.846373] mt7921e 0000:05:00.0 wlp5s0: renamed from wlan0

fludizz@pauwel:~$ ip -6 addr show
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 state UNKNOWN qlen 1000
    inet6 ::1/128 scope host
       valid_lft forever preferred_lft forever
3: wlp5s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 state UP qlen 1000
    inet6 2a10:3781:3fbd:xxxx:xxxx:xxxx:xxxx:xxxx/64 scope global temporary dynamic
       valid_lft 86395sec preferred_lft 14395sec
    inet6 2a10:3781:3fbd:xxxx:xxxx:xxxx:xxxx:xxxx/64 scope global dynamic mngtmpaddr noprefixroute
       valid_lft 86395sec preferred_lft 14395sec
    inet6 fe80::xxxx:xxxx:xxxx:xxxx/64 scope link noprefixroute
       valid_lft forever preferred_lft forever

fludizz@pauwel:~$ ip -6 route | grep ra
2a10:3781:3fbd::/64 dev wlp5s0 proto ra metric 600 pref medium
default via fe80::xxxx:xxxx:xxxx:xxxx dev wlp5s0 proto ra metric 600 pref medium