Their keypairs are for the secp256k1 curve, which Ethereum also uses. That means you can derive an ETH address from their publicly accessible signing keys.
Works just like the mobile app.
Install this app on your iPhone: tap the share button and then Add to Home Screen.
Tap the Share button
in Safari's toolbar
Select "Add to Home Screen"
from the menu
Tap "Add"
The app will appear on your home screen
Enter your Bluesky handle and app password to unlock posting, likes, and your Following feed.
Need an app password? Open Bluesky, go to Settings > App passwords, and create a new one.
Sign in with your Bluesky account to unlock posting, likes, and your Following feed.