Cut and paste this URL to share the unmodified register and value:
https://regviz.com/r/Silicon Labs/SiM3_NRND/SIM3L168_A/CLKCTRL_0/CONFIG#0x0
PMSEL=PM8_DIS
Configuration Options
Power Mode Select.
0 (PM8_DIS): Power Mode < PM8.
1 (PM8_EN): Power Mode = PM8.
https://github.com/cmsis-svd/cmsis-svd-data