New bios was released for some boards. Give it a try.
Can confirm, any undervolt on this board will result in severely degraded performance. My 13500 on this board will consume 150-155W on load with high temps >80'C, Cinebench R23 Multi ~21000
With other B660 ITX board from other brand (B660GTN), I can undervolt it with -0.115v offset, and get 115W on load with the same ~21000 CB R23 Multi score, temperature was in the low 60s.
It seems like when the Asus B660I undervolted, something 'interrupts' the CPU under heavy load, so it is still showing full 4.5GHz all core, but it is not working as it should. CB score dropped from 21k to 13-15k. The voltage didn't really change either.
Please fix it, undervolting is extremely important for any experienced ITX builder.