That wasn't open source. The code used by bitcoin is public - anyone and everyone can, and does, scour it for bugs and backdoors.I'm sure, if you have any familiarity with software, you're aware of the AN0N app. The app was available on the Google and Apple stores since 2018.
A hypersecure text-based communication app that would allow people to send highly encrypted instant messages whose content couldn't be read or the users identified. Like cryptocurrency, its a highly useful tool for those engaged in less than legal enterprises.
It was revealed earlier this year that the app was actually created by the FBI who could de-encrypt all the messages in real time and used the app to monitor the communications of thousands of criminals.
Again, I appreciate your skepticism - I'm skeptical too, or I'd have my entire retirement in bitcoin. There's no guarantee it will retain its value, and the banksters and governments will be doing everything in their power to crush it. I'm just saying that the concerns you're raising aren't valid.