My highlights and notes from articles and PDFs are scattered everywhere with no way to search them

I read a lot — articles in the browser, PDFs, ebooks — and highlight things I want to remember, but every app keeps its highlights locked inside itself. Six months later I can't find that one quote I saved because I don't even remember which app or which article it was in. I want one searchable place all my highlights land in, regardless of where I read them.