Cut and paste this URL to share the unmodified register and value:
https://regviz.com/r/stm32/stm32wl3/STM32WL33/DYNAMIC_REG/FAST_RX_TIMER#0x0
FAST_RX_TIMER register
Fast RX termination timer value (corresponding to the delay to measure the RSSI and to let the HW check CS flag information)
Enable the Fast RX Termination feature
https://github.com/modm-io/cmsis-svd-stm32