Okay, figured out a workaround: after installing Rainbow wallet, selecting it from the "Connect Address" menu, I got a pop-up with apps that can open walletconnect links (the WalletConnect button would do nothing), and Ledger Live was listed there, allowing me to open the link and connect my ledger to warpcast.

co-founder of casaliz.co.jp, work in software/embedded/VR, interested in learning ethereum protocol and L2 development, farcaster.id/hosaka

Warpcast for web added a function to connect an address: https://warpcast.com/dwr/0x6cf8ff