The stock OS doesn't use it for any of the kernel or most of userspace. It only uses it for specific processes where they're explicitly enabling it in that mode and apps explicitly opting into it. Nearly no apps are explicitly opting into MTE. On GrapheneOS, we dealt with third party apps by always using MTE with apps opting in, apps with no native code of their own and apps in our compatibility database. For the remaining apps with native code and no MTE opt-in, we have a per-app toggle and a global toggle to change it to opt-out instead of opt-in. We have user-facing MTE crash notifications providing a traceback to report to developers. We plan to significantly expand our compatibility database to always enable it for more apps like Signal but we're being cautious about that due to the potential for apps to ship a memory corruption bug occurring in regular use which not prioritizing fixing it. WhatsApp is an example of a widely used app which mostly works with our MTE integration but sometimes crashes in regular use and Facebook hasn't taken the issue seriously despite MTE not having any false positives.