Fedora 33 Workstation works great except for controlling the brightness on my 2013 iMac (iMac14,1). This computer uses the Intel Iris Pro Graphics 5200 as its GPU.
After entering a GNOME session (both Xorg and Wayland), I can move the slider but the brightness doesn’t seem to change. I tried appending several acpi_backlight boot parameters with no luck, but then I noticed that when I suspended the machine and afterwards woke it up the slider would actually control the brightness properly.
Checking the Problem Reporting application shows that xorg-x11-drv-intel crashes after waking the computer from suspension because of “WARNING: CPU: 3 PID: 2350 at drivers/gpu/drm/i915/display/intel_display_power.c:4850 hsw_enable_pc8+0x61e/0x640 [i915] [i915]”.