Share to/from WhatsApp has a feature where you can send a message from WhatsApp/email/Telegram/Facebook messenger and automatically make a note. It accepts photos too.
Unfortunately, the data can’t be exported yet, so that site appears to have no use.

Still, there should be a way to set this up for Obsidian, possibly using existing tech of some sort. All we need is a bot that can read messages and save them locally into the vault.

you are saying that has a dedicated WhatsApp phone number that you can write to?

Yes. I think they do

The main difference between and all the other Cloud based solution like, notion, … is that is offline by design.

This means that can be free because the cost of the server are lower.

We could not even create a free plugin for it because the API of WhatsApp are not free