Not sure if you noticed but the OpenWRT 21.02.x series (based on mainline kernel 5.4 series) is affected, and these guys generally know their game when it comes to wireless on Linux. So much so that I think the mainline kernel mt76 driver is actually maintained by an OpenWRT developer.
https://openwrt.org/advisory/start
Maybe MediaTek has shipped some modified versions of OpenWRT using this "wappd" thing to their B2B customers (as part of the SDK perhaps?) and are now advertising those as vulnerable.
The OpenWrt folks generally have good enough taste not to ship any drivers or userspace junk from vendor SDKs, though they do have a fair-sized set of backport patches on top of the (somewhat elderly) mainline kernels they do ship.
I'm running up-to-date mainline on my routers, not OpenWrt kernels. The mt76 support in 6.11 (and previously in 6.9 and 6.10) is complete enough that I don't need to carry any patches at all over what's in Linus' tree.