When I run bitcoin-qt, it sets up a default wallet. When I ask it for the recipient address for this wallet, I was expecting something like 1FGasdfasdfasdf123asdfasdf. However what it actually provides is BC1QNZasdfasdfasdf... In fact there seems to be no way to induce bitcoin-qt to divulge an address in the form of 1FGasdfasdfasdf123asdf... Can someone clear up what the BC prefix is all about? I'm using the main Bitcoin blockchain (350 GB in size), not Bitcoin Cash..
This is a BIP173 native segwit address.
If you unselect the "Generate native segwit (Bech32) address" checkbox in bitcoin-qt, you'll get a P2SH 3xxx address instead. Most senders these days support sending the BIP173 addresses though, which are cheaper for you to use.
The GUI no longer supports creation of legacy 1xxx addresses by default. You can override this by starting bitcoin-qt with the
-addresstype=legacy command-line option. There is no reason for preferring these, except for test purposes.