On iPhone, Safari can't hand links to a website. A shortcut closes that gap: afterwards “To Wishonaut” sits in every app's share menu – one tap and the wish is on your list.
Open the Shortcuts app and tap the plus in the top right.
Tap “Add Action” and search for “Open URL”.
Enter this address, then append the “Shortcut Input” variable right after it:
Tap the name at the top, then “Details”, and turn on “Show in Share Sheet”. “URLs” is enough as the input type.
Name it “To Wishonaut” and save. It now appears in every app's share menu.
On Android you don't need this: just install Wishonaut via the prompt on the start page – it then shows up in the share menu by itself.