Cut and paste this URL to share the unmodified register and value:
https://regviz.com/r/Silicon Labs/Series1/EFR32ZG14P/EFR32ZG14P231F256GM32/USART1/ROUTEPEN#0x0
I/O Routing Pin Enable Register
RX Pin Enable
TX Pin Enable
CS Pin Enable
CLK Pin Enable
CTS Pin Enable
RTS Pin Enable
https://github.com/cmsis-svd/cmsis-svd-data