For a personal knowledge base? I would stay far away from anything proprietary for personal notes. I love logseq though I'm increasingly worried it's abandonware
Obsidian is at least storing in markdown. Although some plugins probably add additional formatting that isn't standard.
My use case isn't likely to be a personal knowledge base, I've just never had any traction on that sort of thing beyond a blog/microblog. I'm wanting to use something specifically for organizing the building of a shop/ADU: todo lists, pinterest-like inspiration boards, costing spreadsheets...
https://anytype.io/ is the open-source CC of Notion AFAIK.
You don't lose anything from the proprietary nature of Obsidian because it's just markdown files all the way down.
For the sake of staying a computer nerd I decided to put all my notes in a private GitHub repo with help of a local 5b Gemma4 LLM. Is working extremely well. It doesn't matter in what format i type. I Use opencode for entering new notes.
Logseq isn't abandonware - they're in the process of rebuilding the app from the ground up to be database-driven, rather than house-brand Markdown as the source of truth and a database constructed from the files afterwards.
I'm not saying it's the most likely project to survive, but they've been working in quiet mode for a good while now.
Logseq was captured by VC a long time ago. They switched from open files to a database, their synching product is closed source (not selfhostable), and they have built-in telemetry.