I have various computers a fast connection most of the time but since
the lock down facebook and youtube pages don't fully download is this
because there are so many people on line that nornaly wouldn't be ? ...

Could be, I have not noticed any slowing down nor long delays downloading streaming services but then we are on FTTC with just a few hundred yards along copper wires. Quite a few are on VM and most still on ADSL round here so it is hard to gauge, but I do recall when we initially were on ADSL at busy times downloads could take a little longer but no real trouble with web pages or YouTube.

Richard