That's what I started with originally, but it's not offline and stores all data on their servers.
Something like Workflowy but offline or self-hosted would be brilliant.
I originally came from Roam and was really happy to find an offline alternative in Logseq. I've since moved to Obsidian, though.
Obsidian works well, but I still feel like my brain works best with the outliner-style workflow that Roam and Logseq offer.
I have heard of https://outl.app/ but when I tried it out, it still seemed in a very early stage (and heavily vibe-coded, which I also don't enjoy).