First, you can try restarting your iPhone 12 to see if you can resolve the wifi and Bluetooth connection issues. If the problem persists, you can try to update the phone system version, and sometimes a software update may fix these issues.
Alternatively, you can try to restore your phone's network Settings to factory Settings to make sure there are no problems with the Settings causing connection problems. If the above methods do not work, it is recommended to contact Apple customer service or go to a professional repair shop to detect and repair the hardware problem. I hope I can help you solve your problem.