I was able to get 1Password to work with CVS, but only as a separate device. I was on my computer and when I chose a separate device, it brought up a QR code. I scanned that with my phone camera and it recognized the passkey add for 1Password such that my 1Password CVS item now shows a passkey. BUT, when I try to login to CVS using it, it doesn't prompt 1Password, it just brings up the QR code. I then scan that with my phone camera and 1Password on my phone authenticates and gets me in.
And then ....I can't find any passkey setting on the CVS website to remove this passkey so that I can either have none or try again. So, that's fun.
I'm sure that's not the idea of how this should work. I thought I'd share the different experience from what has been reported.