Related task: T138727
By default modules target desktop only. They must explicitly add "targets" => [ "desktop", "mobile"] to their ResourceLoader definition.
Modules that are added to the page without targets are silently removed and trigger warnings.
Longer term we would like to remove the targets system, but before doing that we need to knowingly make decisions about the code we maintain and where it should run.
If the module works on mobile, is small/sensibly loaded so as not to cause potential for performance regressions for end users it should define targets.
If the module does not work on mobile it should be conditionally added to the page so it only runs where needed. See instructions on T235712 for potential loading strategies.