canLoadOpaqueURL() was replaced with navigator.canLoadAdAuctionFencedFrame() in 2023, and calling it has resulted in a deprecation console warning ever since pointing developers to the new API. It does not make sense to have the function attached to `HTMLFencedFrameElement` and instead should be attached to the `navigator` object (which contains other fenced frame + ad auction methods).
This can already be done with its replacement: `navigator.canLoadAdAuctionFencedFrame()`. Because the `navigator` object contains other fenced frame and ad auction related functions, it is better to have this API live there.