Indeed it is, as well as Paypal where supported too if your account falls under the right jurisdiction.

Correct, my message was to confirm that payments can and do work on GrapheneOS so long as there is an implementation available to you.

Now that you've mentioned the watch if it is a WearOS device capable of Google Pay then yes it can be used for payments independent of having Google Pay on the handset.

Is that a question specific to Swissquote or in general? If in general yes NFC payments are available on GrapheneOS so long as your bank or provider provides their own implementation such as ImagineCurve's Curve Pay.