Some BIOS upgrades will not allow a downgrade depending on the version. This thread at reddit may help though as it does address your undervolt question.
____________________________ System Model XPS 15 7590 OS Name Microsoft Windows 11 Home System Type x64-based PC BIOS Version/Date Dell Inc. 1.22.0, 06/06/2023 ____________________________ Hello, for a few weeks now, my laptop is overheating just being in idle. I'm guessing it is due to BIOS updates, so I was thinking about Undervolting the CPU. Since my BIOS ver. is 1.22.0 I can't undervolt it, so I have to downgrade the BIOS ver. I downloaded ver. 1.12.0 from the Dell support site. Everytime I try to install ver 1.12.0 the laptop restarts, the DELL logo displays and I get the error message "BIOS Update blocked due to unsupported downgrade" and my BIOS ver. stays at 1.22.0. From what I found in other threads, I already did the following: In BIOS settings: - Intel Virtualization Technology  is toggled off - BIOS Downgrade is toggled on , but still no successful downgrade.  
XPS 15 7590, overheats in idle, cannot downgrade BIOS