Hello Mark,
Please create one new project , then add the UART to configuration .
I test your project on my side , it also have error when build , while i create
a new project , add the Serial_LDD component , enable the interrupt, it have no error when build.

I don't whether there is some problem when you create and configure the project.
I attach my project.
Hope it helps
Have a great day,
Alice Yang
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