Hello Sadoka,
Yikes! Those are very high temps! Hopefully we can reduce them and possibly even increase performance at the same time.
Versions 306 and higher of this BIOS image contain the undervolt lock. Downgrading the BIOS before a mod will be difficult, so I think the best courses of action here would be the following:
1.) I will compare the 305 and 306 versions of the BIOS image and see if I can figure out what locks undervolting. Maybe I can remove the lock in an actual BIOS dump of your computer after you perform this second step. Regardless of whether this I can remove the undervolt lock, I can still unlock advanced settings.
2.) In the meantime, you will need to order the CH341A hardware programmer (not all computers require this, but this one does). This will allow us to get BIOS dumps from your computer and flash the modified BIOS image. I will perform the actual mod on a BIOS dump to preserve specific system details such as UUID, Serial Number, MAC addresses, etc. which are stored in modern UEFI images. This dump will also work as a backup in case of the off chance anything goes wrong.
Here is a link to one place (out of many) that you can purchase a CH341A and a SOIC8 adapter:
https://www.amazon.com/gp/product/B07V6W...00?ie=UTF8&psc=1
Please note that there are some cases where the included clip won't work due to an inadequate connection to the chip. You will know when we start trying to get BIOS dumps. If that happens, you will need to additionally purchase the Pomona 5250 clip, as well as 8 female-to-female jumper cables to attach the new clip to the programmer. This is what the clip looks like (you can also find it elsewhere):
https://www.amazon.com/CPT-063-Test-Clip...B00HHH65T4
Here an option for purchasing the jumper cables:
https://www.amazon.com/EDGELEC-Optional-...les%2B50cm&qid=1637356511&sr=8-3&th=1
^On this page, choose Female-to-Female or Assorted. For the size, I recommend at least 40cm (15.7 inches).
Here are instructions on how to set up the CH341A programmer physically:
https://www.win-raid.com/t4175f16-GUIDE-...ammer.html
Here are instructions on how to use the AsProgrammer hardware programming software:
https://www.onetransistor.eu/2018/11/use...ndows.html
Let me know when you get the BIOS chip programmer and I can help guide you through the process of obtaining a BIOS dump if you need further assistance.