◇ Could this help me?
Yes. The failure mode described is real and the fix is correct: in Next.js it is the module graph, not intuition, that decides what reaches the client bundle, so a server helper co-located with a client component can drag a connection string into a public file. Step three is the one that actually proves the fix, because it inspects the shipped output rather than trusting the reorganization. General practice, with one addition the video omits: any credential that ever shipped to a browser should be treated as compromised and rotated, not just hidden.
Audit this Next.js codebase for credentials leaking into the client bundle. First, list every file that touches the database, API keys, or environment secrets, and tell me which of them also export or import anything that renders in the browser. Second, propose a file split that keeps server functions in modules sharing no exports with client components, and show me the import chains you are breaking. Third, run a production build and search the emitted JavaScript for my database hostname, connection string, and each environment variable value, and report any match as an already-exposed secret that needs rotating. If you want to add the server-only package as a build-time guard, research it first, tell me what it is, who maintains it, and whether it is reputable, and install it only after I approve.