Looking for a tool to semantically search a massive codebase - I will not promote

I have a million-line codebase that no one fully understands, and debugging is a nightmare. I need a tool that indexes the code, creates vector embeddings, and lets me search for relevant code using natural language (e.g., "correlation matrix plot coloring"). Ideally, it should be low/no-code to set up and have a GUI for searching. Does anything like this exist? Looking for paid or open-source options.