Why does Bisq not allow sending bitcoins to a BC1 address?
Bitcoin addresses that start with bc1 are native segwit addresses. It’s not possible to send/receive funds from a native segwit address to a “legacy” P2PKH address (i.e., those starting with 1).
Updating Bisq to support bc1 addresses is a highly complex and time-consuming endeavor and probably won’t happen until Bisq itself is rebuilt in a fundamentally different way.
There was a tweet about this earlier today: