I just switched off my router and started Troy without even getting any notice, but then I was signed in already.
Signed in and offline works
Exiting the launcher and trying again then prevented me to start Troy - see the two self explanatory pics, it seems Troy is one of the games that cannot be played off line. Seems sign in is mandatory.
Not signed in and off line does not work
..
Looks like I won't be getting Troy, after all.