How do I use the microphone of the Droidcam work
The error ./install-dkms: line 32: dkms: command not found is important, and is why later things aren't working. You need this command to work successfully for Droidcam to work. See this post for what dkms is.
To install dkms, run sudo apt install dkms. Reboot, and then try the script again.