So I did test this with the oldest ASRock microcode from original 3.02 bios for ADL, on 12600 and 13600k as well (but with the 8xx bios ui).
The first issue seems to be whether the vendor will display voltage control for Locked chip, and in this case it appears that ASrock decided not to continue to do this on subsequent bios after 3.02, but they do display it for unlocked chip. This is either because locked chip doesn't support it, or some policy related reason (of steering the user to be on zX90 chipset in order to get voltage control) as a bit of research appears to show that vendors tend to leave these features out on purpose on the lower end chipset. If this is correct then you would need to buy a "K" chip to get this voltage adjustment functionality in the first place (and then.. disable cores or do a lot of tweaking).
The second issue is while K chip does cause the voltage offset controls to re-appear (as was in original 3.02 bios) and allow setting negative offset, they still do not appear to do anything. The reason is probably a bit complex as Intel has done a bunch of things to discourage ADL and Raptor chips from running at lower voltage. So it's hard to say if it is a result of Intel's bullshit, or just some integration issue from ASRock. One thing I forgot to test is the 13600k with the latest 12xx bios, just to see if something changed and the adjustments were now magically supported. So of someone also has a Raptor chip, they might check to see if there are voltage controls on latest bios 12xx.
I emailed ASRock to encourge them to adopt the same measures that the other vendors are doing on b660 to cure Intel's bullshit: allow old microcode swap, disable CEP, disable UV protection, and put in Load Line control (basically the alternate/budget way of undervolting, which will work universally even on a locked chip). But of all the 5 e-mails I have sent to ASRock over the last year, maybe one got a response.