Most likely the issue is due to the Windows Store version of the game. Among other problems, that version unfortunately has crippled scripting/modding support because it's so heavily locked down (can't edit files etc).
Because that version is so locked down, simply manually disabling the nukes instead is sadly not possible either.
You could use the multiplayer lobby to play vs AI, although this will unfortunately introduce the typical multiplayer lag even if you're the only human player.
One other unconventional workaround you could try (but which is obviously quite clunky) is to use the
in-game cheats (in a singleplayer game) to give yourself Missile Shield:
cheat tech missile_shield on
I'm unsure if that would work reliably or not as tech unlocks, but it's more likely to work than not.
Alternatively, if you grab it on Steam instead then you can gain full access to scripts / mods again (at least for singleplayer). If cost is an issue, it regularly goes for ~75% off retail price.