Not using Kagi because its an American company is valid. But people are too used to products that are free because they make the person using them the product. There is still a transaction with a free product.

Kagi is not free because they respect your privacy and don’t sell your data.

I use Obsidian with the obsidian-live sync docker container to sync data between devices instantaneously. It is not open source but they store plaintext markdown notes and its extendable with plenty of open source plugins.