Yes Galileo supports encryption. But as far as I know it’s not in use. Has been trialled only. But I know all Airbus aircraft only support GPS satellites and nothing else (yet). I assume Boeing, being American would be the same then.

As far as solutions go, an aircraft can navigate fine without GPS. It can update its position from ground navigation aids and if they are not available it can still Dead Reckon very well. The navigation error very slowly grows until it’s out of the black spot and can use GPS or navigation aid to increase its accuracy. But this navigation error on the time frame of say an hour is a matter of kilometers at most, not dozens.

It could be that Google is releasing this incrementally. It seems a bit random who gets it and who doesn’t