GPU/VMEM stuck to full speed when 2nd display connected

RX 580/i9 10850k on Asus Z490-p, Big Sur 11.1, OC 0.6.5. When 2nd display is connected (DP or HDMI), there's no power management on the GPU. It's stuck at max frequencies (1340/2000 MHz) at all time. With only one display connected, it downclocks properly up to 300/300. Tried Radeonboost.kext to no avail (it did help with this issue earlier in Catalina).