If a Contractor provides a more expensive door than what’s written in the Works Information, and the Employer chooses to keep the new expensive door as it reduces maintaining in the future. What is the process that should be follow here?
The answer may be nothing, as if the Works Information stated to install a certain specification as a minimum and this door exceeds that (but complies) then this would not be a defect. If however the WI specified a certain door and this is not that (even though better) then either the Contractor corrects the defect i.e. installs the correct door, or the PM can choose to accept the defect which would normally come with a cost saving if what had been provided was not as good. However in this case it is better, so the PM could accept the defect and give an instruction changing the Works Information in line with what you have installed.
There is certainly no obligation on the Project Manager to agree to pay you more for something they did not ask for.