For internal mic, can you make sure microphone access in general isn’t turned off? System Settings > Security & Privacy > Privacy Controls > Microphone Access.
Then also you can go from Privacy Controls to “Permissions Manager > Microphone” to check all apps with Microphone access and make sure apps you expect are allowed.
Next for your bluetooth devices, you can set the “Type” of bluetooth device, possibly this may confuse something if not correct (but if “unset” it should be fine). You can find the setting under System Settings > Connected devices and then the gear next to the device. You can make sure it is allowed for “Phone Calls” and also set “Audio device type” but these would just affect your bluetooth devices not your internal mic.
Sorry I am traveling on holidays so will have spotty replies at best for another week.