I'm usually in a terminal, so I use vimwiki (https://vimwiki.github.io/) - it supports markdown, adding pages is trivial, and vim tags or CLI tools like grep makes it easily searchable.

It lives in a private NextCloud instance, so everything's available from my laptop or phone (although editing markdown on a phone is no fun).

Edit - this is great for detailed note-taking; I also use a custom command-line tool to capture ad hoc notes, ideas, and suggestions without opening vim. They go into a YAML file right now; tooling in process to pull them directly into the wiki, so everything's in one place.