The Realtek switches in OpenWrt use a different downstream driver, which does implement the MDB methods: https://git.openwrt.org/?p=openwrt/openwrt.git;a=blob;f=target/linux/realtek/files-6.6/drivers/net/dsa/rtl83xx/dsa.c;h=69151b2f6bb4d077e8c8a0b619bd4ef6101773f8;hb=refs/heads/main#l2219
However, currently multicast snooping is somewhat broken for all DSA switches. Multicast snooping requires that all multicast is flooded to multicast router ports (such as the port which has the multicast querier behind it). The bridge implementation in the kernel does that properly, but it is not implemented in DSA.
This has been discussed on the kernel mailing list. And here is the OpenWrt patch series which sparked the discussion.
Someone made an attempt to fix this in the kernel, but it did not get accepted.