Screen brightness not working on Dell Inspiron 3000 (Intel Iris Xe) — value changes but screen doesn't dim

Hardware: Dell Inspiron 3000 series (TigerLake), Intel Iris Xe integrated graphics, NVIDIA GeForce MX350 (hybrid graphics) OS: Ubuntu (latest version) Kernel: 7.0.0-29-generic Brightness control stopped working about a month ago. It works fine in BIOS/UEFI, but not in Ubuntu — no update or upgrade caused it (checked apt/unattended-upgrades logs, nothing relevant around that time). Symptoms:…