The "cross platform" bit is completely irrelevant. The user friendly and strong security (there's no such thing as bullet proof security) points are certainly achievable with a little effort.
Cross platform is important for official matters because allowing a platform specific tool means the government,legal community and fellow citizens are also expected to use that platform to interact with content made or consumed by that platform specific tool.
Sorry but you're still missing my point (though I didn't really make it all too clear).
User friendly design is about understanding user behaviours, UI/UX, etc. It's about designing sane workflows and user interfaces. Whereas writing cross platform code is a technical complication regarding the internals of a particular application. The crossover is between cross platform development and user friendly design is just which UI toolkit you choose to use (ie Electron, Qt, native platform-specific widgets, etc?) and even that is really just an implementation detail rather than a fundamental roadblock in designing user friendly applications.
Thus the requirement for something being user friendly shouldn't affected by the requirement for something being cross platform.
This is why I say the cross platform point is irrelevant. Not because cross platform solutions aren't important but rather because they're not the reason many solutions aren't user friendly (the reason is much more simple than that: they were designed by technical people to be used by technical people).
The "cross platform" bit is completely irrelevant. The user friendly and strong security (there's no such thing as bullet proof security) points are certainly achievable with a little effort.