I can’t see if your AMD CPU is zen2/3 but maybe you have to add amd_pstate
into mkinitcpio.conf like:
# vim:set ft=sh
# MODULES
# The following modules are loaded before any boot hooks are
# run. Advanced users may wish to specify all system modules
# in this array. For instance:
# MODULES=(usbhid xhci_hcd)
MODULES=(amd_pstate)