I feel pretty sure that I'm only scratching the surface of how the text-based tool Obsidian can be used, but it's worth me adding my small amplification of a very useful tool. I stumbled across Nick Milo's "Linking your thinking", and then from there, various discussions of Notion vs Roam Research. Then a few mentions of Obsidian as a PKM (or Personal Knowledge Management) system.
To call my own usage of it at the moment a system would be laughable but it's the first application I open on my computer each morning, and I have it set up to create a daily note, simply date-stamped, into which I can paste tasks to do, little snippets of text, screenshots.
If you want to see how it can be used to a much greater extent, check out Bryan Jenks, particularly his video Here is how I use tags and links in Obsidian to manage my Zettelkasten
I love the fact that "it's just Markdown" - i.e. a very clever rendering of simple text files. Although there's a cloud storage option, you can equally keep it locally on your computer or use a synchronisation tool like iCloud or OneDrive. I have at points experimented with the option of synchronising with GitHub, but it felt a little noisy to me.