I don't use WhatsApp, I use Signal, Messenger, iMessage and Snapchat (yes I know but these things have inertia). I'm not exactly alone here. You'd need to write third-party clients for all those apps as well.

Meta had a perfectly fine WhatsApp client for KaiOS phones, they disabled it.

Unfortunately that EU WhatsApp interoperation thing isn't really what we wanted. I assumed it would mean that you would be able to communicate with WhatsApp contacts using a non-WhatsApp app (kind of like Pidgin back in the day).

Meta obviously don't want that and they've done a sneaky thing to make it useless: if you connect a third party app to WhatsApp, from that third party app you can only chat with other WhatsApp contacts that have also connected the same third party app to WhatsApp. So if you write your own WhatsApp client that runs on this low power phone it will be completely useless because to chat with your friends they would all have to manually connect their WhatsApps to your client, which of course they won't do.

See https://developers.facebook.com/m/messaging-interoperability... - check the `WhatsApp Messaging Interoperability User Experience - Android`

I guess we'll see if the EU lets this stand but my guess is they will.