Cut and paste this URL to share the unmodified register and value:
https://regviz.com/r/Silicon Labs/EFR32MG24A120F1536GM48/CMU_S/SYSRTC0CLKCTRL#0x0
No Description
Clock Select
1 (LFRCO): LFRCO is clocking SYSRTC0CLK
2 (LFXO): LFXO is clocking SYSRTC0CLK
3 (ULFRCO): ULFRCO is clocking SYSRTC0CLK
https://github.com/cmsis-svd/cmsis-svd-data