Yes, correct. The new feature is called "Intel Undervolting Protection". It was silently released some time ago. Initially, it was intended to block undervolting using apps like ThrottleStop, but in practice, it can also break the BIOS undervolting. The options may still be in BIOS, but once you apply even a tiny undervolting, the system may become unstable, stop booting, or show a huge performance drop.9.5 works for me with Gigabyte B660M Gaming X and 13600k. I had to downgrade bios to the first version that supports 13th gen, dated 2022 August, and it started working. If I flash newer bios, it doesnt work. Seems like Intel introduced some undervolting lock later on.
You may find more details here: Inter Undervolting Protection: The Whole Story.