I don’t think there is a single NFT marketplace that supports smart contract wallets. 

In fact, is there any dApp at all that implements EIP 1271 for their login?

Building @onit to be the home of multiplayer crypto  🌀 @variant VFF '23 💡 writing: https://mirror.xyz/jamesmccomish.eth

btw I tried to signup for Onit just now, but the "apply" form fails for me with what appears to be CORS error.

This is such a pain. We struggled with this over a year ago building a previous version of Onit. 
There are ways to make listings as a SCA using OpenSea, but no nice way via the UI.