The APT error is most likely a result of using PPAs - some PPA you use (probably the one with simple64) provides libxapp1 2.8, but doesn't provide happy at all, so you end up falling back to the much older version from your distro's repositories. But xapp needs an exact version of libxapp1, so you get this error.
That said, if the simple64 PPA doesn't provide the xapp package, then it perhaps isn't required and the module should be provided by libxapp1 (and the problem is something different). Or maybe it comes from a completely different PPA - I believe apt policy libxapp1
should tell you where it's coming from.