And try to define "major distros" in a way that actually means anything viable.
If you just want to count users, then that would only be Android (everything else is a rounding error.) After Android, that would be Yocto, and then Debian. All distros after that are mere fractions of overall users compared to those 3 by number of running systems alone.
If you want to count it as "$ spent on Linux" then that cuts out Android and Yocto and Debian as those distros are free, and would focus purely on the tiny installed base of paid Linux systems, and cut everyone else out.
So what is a fair way to do this other than "we notify no one, and tell everyone to always update their systems to the latest stable releases that we support."
Especially as there is no way for us to determine your use case (i.e. if a specific bug is a vulnerability for you or not.)
Edit: for context, I work in embedded and the aarch64 version (PR #42 in the repo) has successfully popped every device I've tried it against except one where I have a custom kernel to work around a driver issue and (looking back at my git logs) accidentally forgot to enable the user-mode API for alg_aead specifically. Lucky mistake.
Given the potential impact a severe security issue in the kernel (like this one), it seems that the only process that is acceptable for government agencies of various countries (that deal with intelligence and national security) is to either keep secrets from everyone, or disclose them to everyone.
Otherwise, the entities on the priority disclosure list would basically have free access to zero day vulnerabilities. Then every country with a national intelligence agency would invent a distro and try to squeeze themselves onto that list, and things would become very political and ugly if the agents of any country can't get into that list...