Cut and paste this URL to share the unmodified register and value:
https://regviz.com/r/stm32/stm32f1/STM32F101/UART4/SR#0x0
UART4_SR
Parity error
Framing error
Noise error flag
Overrun error
IDLE line detected
Read data register not empty
Transmission complete
Transmit data register empty
LIN break detection flag
https://github.com/modm-io/cmsis-svd-stm32