Xcode not opening after updating to MacOS Catalina

What worked for me was updating Xcode in the App Store. After that I was able to install the additional components successfully.

First, try updating Xcode through the app store

As a last resort, you can change your MacOS Date to

1st October 2019

I set my system time to 1st October 2019, the date when the certificate was still valid. Then, I opened Xcode and followed the component install. This went well, and now Xcode works again.

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