Cut and paste this URL to share the unmodified register and value:
https://regviz.com/r/Silicon Labs/EFR32BG22C224F512GM32/GPIO_S/USART1_RTSROUTE#0x0
RTS port/pin select
RTS port select register
RTS pin select register
https://github.com/cmsis-svd/cmsis-svd-data