I was on a domestic flight in Europe two months ago and there was no such announcement. They were probably just being nice and saving you some battery.
But there is absolutly no reason to turn it off because of any saftey concerns with the plane.
Even on reddit that could easily be circumvented by using a different frontend or app. And it's something that can easily be implemented by frontends/apps for lemmy.
You could have a bot check the replies for certain words without anyone having to read them. But I'm pretty it's just an empty threat. I tried it out once and nothing happened. And I made sure to hit all the common keywords.
I have a DS2422+ and even that only has 2 USB ports. But you can expand them with a USB-hub. I had 5 external drives connected over a single port without issues.
Synology’s limited list of “approved” HDDs.
You can use this script and put it as a scheudeled task "on boot". It will automatically add all your harddrives to the list of verified drives, disabling all warnings and errors with it.
So ... what is your question?