On a personal note, please don't do this. I understand people choosing their preferred pronouns, but don't force it on others unless they have stated preferred pronouns too.

Quick edit: went and looked at the developer team (https://obsidian.md/about). It's actually a man, a woman and two cats, so "their" is clearly appropriate.

Joplin, as an example, allows syncing via WebDAV. Which you can easily self host.

I know that Joplin works differently. Obsidian also has integrated sync capabilities, but it’s a proprietary protocol and you can’t self host it. And I guess this is a design decision of the authors. To sell their service. They probably need some money to pay their bills.