I would assume so, but I'm not 100% sure. I personally haven't yet messed with Passkeys much aside from use on a couple of sites that have implemented them.

My working assumption is if you wanted to use a new browser, you'd have to attempt to log into the service with the new browser. When the Passkey flow prompts you with a QR code to scan, you'd have to use your iPhone/iPad to scan that QR code to allow entry. What happens after that, I have no clue.