eBay offers no passkey option

1P_Dave My device is a Google Pixel 7 running up-to-date 14 on which 1Password is my exclusive autofill, password and passkey provider.

Do you have a public link to the "Unable to create passkey" issue which you reference?

I've not started to work with eBay support on this and despite a strong inclination and long history of trying to help organisations to improve their technology and communications, I am reticent to engage their support staff on a substantial bug report as an individual user. Based on the quality of posts and responses, I am even less inclined to try to have this addressed by their Community.
If and when I see a significant effort to get eBay and PayPal to improve their authentication processes, then I'll be happy to contribute to it.