Watchtower says Passkeys available however cannot see Passkey on suggested sites?

Unfortunately, the Passkeys availability display from Watchtower is very unreliable, if you don't live in the US. Also if you don't use the most supported device with the most supported OS (whatever that is, this differs from company to company).

Actual passkeys availability is often country specific (US gets first, everyone else get it months/years later), and it's often specific to some device with some device OS and specific browser.
Paypal for example first wasn't available in Germany for months, and now it's available but insists on using a mobile device for passkeys and doesn't accept a passkey from my Windows 11 desktop browser. Because of this I don't use a passkey for Paypal, which is a pity.

I ignore this Watchtower category, because it wastes my time by making me search for the passkey functionality on the sites's security options only to find none or some "unsupported for you" error message.