Need guidance buying Monero using Bitcoin on Bisq

I have a bitcoin paper wallet I want to use to buy XMR. Is this possible without any intermediate crypto?

I only see that I can add an "Altcoin account" which does NOT include bitcoin. Weird ??? I know Bisq comes with an internal bitcoin wallet or something. Do I need to transfer my BTC to this internal wallet?

Also, when I go to the Buy tab, the only "Payment method" listed from sellers is "Altcoins" or "Altcoins Instant", so paying with bitcoin is out of the question ?? Or what am I missing ??