MobileDevice.pkg untrusted, cannot open Xcode after OS X update

Edit and set the date of your Mac as October 1st, 2019.

I didn't have Xcode 11.1 installed and even though I could open and run the 11.0 after the below workaround I could not update to 11.1 as the update always failed. So I have just re-installed the whole app from the App-Store - you could probably also do this instead of the below method.

I have tried setting my system time to 1st October 2019 when the certificate should had been still valid. After that I tried to open Xcode and followed the component install which went well and now I am able to work with Xcode again.

I had a similar problem, where I installed Xcode 11.1, and installed the components and everything within the same folder where I had Xcode 10.2.1. Then, I tried to go back to Xcode 10.2.1 and couldn't opened as it was asking me to install components again, and when I tried I was getting this error.

The package “MobileDeviceDevelopment.pkg” is untrusted.

So, the workaround that fixed it for me was navigating to...

/Users/YourUser/Applications/Xcode\ 10.2.1.app/Contents/Resources/

Then, deleting MobileDeviceDevelopment.pkg and everything went back to normal :)

I hope this helps anyone else with this issue. Cheers!