That's why we don't trust closed source. Are there even closed source Nostr clients?
But also even a noob can formulate these questions, like 'Go checkout the repo of X client. How does it handle the nsec after login? Is it secured enough? Is it being sent to other computers? How is it stored and who can access it?' These are easy questions.
That's what LLMs are also for. For the first time you can now check the source code. Even as a noob. Normalize it.
