This is a big issue. I personally not a big fan of both Slack and Discord. I think something like Github Discussions is much better. As far as other solutions...maybe Stackoverflow can have something like this too for open source projects
I suggest you try JetBrains IDEs depending on your tech stack. They have got an incredible search capabilities. You can search for a word/function where it has been used across project, you can find and replace across the project, etc. It's amazing!