https://triliumnotes.org/ is my clear recommendation. It's quite more powerful than the usual contenders and it may take a while to explore its depths, but it's also not pushing its complexity in your face like Logseq and some others do.

I'm not sure what your needs are, but I've been using Joplin and it works for me.

Tried Joplin, it creates an unholy mess of files. I far prefer the clear format of Obsidian.

Next step is to give up on files/filesystem. As long as it's opensource, there's no lock-in. As long as the storage backend is clean and structured (SQLite or comparable), you actually get so much more (full text indexing, standard querying, ...)

I initially was cautious when going from "bunch of .MD files" to https://triliumnotes.org/ , since it's been pretty great.

Hmmm, it has been years since I last tried it, perhaps it is time for another chance indeed. Thanx.

I am a fan of Logseq [0] as well, although it’s slightly different in that it is mostly for bulleted notes and not long-form prose.

[0]: https://logseq.com/

I tired Joplin, Logseq and Appflowy but ended up with siyuan

You can check my FOSS note-taking app: https://notes-foss.com

This looks impressive. Nice to see a modern, sleek app built with Qt + QML. I moved on from raw Qt after my last job, will take a look at using QML.

Looks great! I'll follow along so I can try it out if syntax-aware code blocks and callouts are ever supported

Great! They will be supported earlier on my non-FOSS note-taking app with a block editor (get-notes.com). So you can follow their as well.