Welcome in the forum.
Datasheet for UART v2.50 states in configure dialog
API control enabled
This check box is used to change parity by using the control register and the UART_WriteControlRegister() function. The parity type can be dynamically changed between bytes without disrupting UART operation if this option selected, but the component uses more resources.
The UART_WriteControlRegister() API is used to change the parity.
The SCB based UART v3.20 uses a different approach: here you need to re-initialize the component using SCB_UartInit(). See datasheet.
Can you please post your complete project, so that we all can have a look at all of your settings. To do so, use
Creator->File->Create Workspace Bundle (minimal)
and attach the resulting file.