"there is no lock-in" is a thing that's said a lot about Obsidian and, as an Obsidian fan, I feel like isn't totally true. Yes, Obsidian just stores markdown files, but it has unique syntaxes, especially if you're using plugins, that aren't transferable. So while I can get my files out, I still have to go through the annoying process of fixing them and getting it working in whatever new system I switch to when I leave. It's still far better than a lot of other proprietary tools, absolutely, but it's also not trivial to drop Obsidian if/when you stop using it

Doesn't seem remotely fair to consider lock-in caused by plugins to be an Obsidian lock-in. If the plugin is storing data in such a way that it's not usable in a tool other than Obsidian, that's 100% the plugin's fault, not Obsidian's no matter which way you look at it.

Also, more generally, any software that has unique features will require "the annoying process of fixing them and getting it working in whatever new system I switch to when I leave", whether it's open source or not. So you're not actually looking for open source, you're just looking for something with perfect feature parity to another program.