ArcGIS Pro fails to start with a serious application error

Description

When starting ArcGIS Pro, the application fails and returns the following error:

Error:
ArcGIS Pro has encountered a serious application error and is unable to continue.

Cause

This is a generic error message that can be returned due to various causes, however when starting ArcGIS Pro, this error often occurs because the user.config file is corrupted.

Solution or Workaround

Create a new .config file
To locate and delete the corrupted user.config file by following the steps below:

Note:
It may be necessary to enable viewing of hidden folders to view the AppData folder in Windows. For more information, refer to Microsoft: Show hidden files.

1. Navigate to the following folder path:

C:\Users\<USERNAME>\AppData\Local\ESRI\ArcGISPro.exe_Url_usrdyax2a4fbxzcclmgcafuxifk3o351\1.4.0.0\

2. Delete the user.config file.
3. Start ArcGIS Pro. 

Rename the ESRI folder
By renaming the ESRI folder to a name other than ESRI, a new ESRI folder is created with a new .config file when starting ArcGIS Pro.

1. Navigate to the following path:

C:\Users\USERNAME\AppData\Local\

2. Rename the ESRI folder (for example, to 'ESRI-old'.)
3. Start ArcGIS Pro.