I’m not sure this is a good solution, but maybe it’s the best “general” fix.

Basically an OS should be able to easily identify when you’re using a platform password field for instance and not interact with the IM (although that causes problems with assistive technologies). But the OS can’t really handle every third party reimplementation of password fields. Presumably a 3rd party solution would be able to rev faster and stay more up to date than the OS. (The risk balance when the OS is involved is higher than for just the IM as if it does break you can always remove the “visor”, but doing so in the os is harder.