Why else would they have reason to block usage of their platforms, if not for such risk? Maybe Putin could be threatening to block access to their platforms, which seems feasible enough, unless such demands are met.
In any case I do think there is enough international attention around Navalny to warrant protection of these executives, should they have been threatened, but my apprehension of all this is theoretical.
Actually it would seem to be in the interest of US national security to ensure that Putin's regime can be challenged by the likes of Navalny, and that US intelligence officers would have reason to support Google and Apple here, but then again I'm willing to assume Putin has his "enablers" in the US public sector to maybe mitigate such efforts. Just speculation though.