You're experiencing issues with linking your WhatsApp account to the desktop app on your iPhone. It's not just you; several users have reported the same problem after switching from Android to iPhone.
One user reported that they were able to link their WhatsApp desktop app after transferring their data from Android to iPhone, but it's not a guarantee that it will work for everyone. Another user mentioned that they were able to link their WhatsApp desktop app using WhatsApp Web, which is a workaround until the issue is resolved.
It's worth noting that WhatsApp support is aware of the issue and is working to resolve it as soon as possible. In the meantime, you can try using WhatsApp Web as a temporary solution.
For more information and to stay updated on the issue, you can check the Apple Support Community thread where users are discussing the problem and sharing their experiences.