If I’m not mistaken you were talking about how things work “on my phone” but I suppose you had in mind that the principle would apply to desktop as well.

In practice it does somewhat come down to how well containerized and locked-down the environment is, so I think the difference does matter. Android for instance sucks in very many ways, but it’s somewhat reliable in usually keeping apps from interfering with each other. There are a few desktops that try to do that, but they’re still not too popular I think. Desktop users are used to having full control of everything. Seems to me the pervasive compartmentalization of everything (it wouldn’t be sufficient for the purposes we’re talking about to put only Signal in a secure container) is accepted as necessary on mobile devices mostly because so many of the apps are terrible.