I agree about "note taking apps" (I use Notion nearly every day) but that's not actually what a Zettelkasten is. It's really a workflow that facilitates thinking and creativity.
Notion is a place I keep tidbits of information... for example a database of my videogame collection, a history of all my previous addresses (I've globe trotted my entire life) or a repository of highly detailed professional notes on complex topics. Even then I'm still not sure that Notion is really a good long term solution since their staff could theoretically access all my private information without me knowing (I've had this confirmed to me via a support ticket).
So, while Notion has extremely good problem solution fit for a lot of my use cases, Notion however doesn't actually help me develop my thoughts on philosophy or help structure my thoughts on how to approach questions I have in my fields of enquiry or help me create content from original ideas. My physical Zettelkasten does.
