If it seems like highlighting extension - it is. However, it designed to work with test cases, works in main document services (Confluence, Notion, Google Docs) and can generate reports. I was working as QA a while ago and we had this obvious and stupid problem with tracking test coverage. After building a prototype creating new cases was like a breeze and I still didn't found alternative so decided to publish my solution. Currently extension is working locally and if free version will have some traction - I'll probably make a team version with collaborative access.

CaseTrace

Visualize your test coverage

Do you use CaseTrace?