Cannot change screen brightness / backlight levels in Ubuntu 22.04.3 on laptop with Ryzen 6800H with Radeon graphics + Nvidia RTX 3070 GPU

Today (12th Dec 2023) I reinstalled Ubuntu 22.04.3 on my Asus dual-boot laptop with the specs "Ryzen 6800H with Radeon graphics + Nvidia RTX 3070 GPU". When I try to change the screen brightness (using FN + F7/F8 key combinations, the brightness 'bar' appears to change but the screen remains at 100% brightness (being blinded by the screen). Output of 'lshw' is:

$ lshw -c video*-display                        description: VGA compatible controller       product: GA104M [GeForce RTX 3070 Mobile / Max-Q]       vendor: NVIDIA Corporation       physical id: 0       bus info: pci@0000:01:00.0       version: a1       width: 64 bits       clock: 33MHz       capabilities: vga_controller bus_master cap_list rom       configuration: driver=nvidia latency=0       resources: iomemory:7c0-7bf iomemory:7e0-7df irq:105 memory:fb000000-fbffffff memory:7c00000000-7dffffffff memory:7e00000000-7e01ffffff ioport:f000(size=128) memory:fc000000-fc07ffff  *-display       description: VGA compatible controller       product: Rembrandt       vendor: Advanced Micro Devices, Inc. [AMD/ATI]       physical id: 0       bus info: pci@0000:05:00.0       logical name: /dev/fb0       version: c8       width: 64 bits       clock: 33MHz       capabilities: vga_controller bus_master cap_list fb       configuration: depth=32 driver=amdgpu latency=0 resolution=2560,1440       resources: iomemory:7e0-7df iomemory:7e0-7df irq:49 memory:7e10000000-7e1fffffff memory:7e20000000-7e201fffff ioport:d000(size=256) memory:fc500000-fc57ffff

As evident from the output above, I am using the Nvidia proprietary drivers activated under 'Software and Updates':

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In the past, maybe a few months ago, using these proprietary drivers enabled me to control brightness. But alas not anymore.

I have also tried to install 'Brightness Controller', but it doesn't change screen brightness either. However, I noticed that the screen brightness can be controlled by changing the value inside the file /sys/class/backlight/amdgpu_bl0/brightness (thanks to my girlfriend's web searching), which originally has value 255. If I change it to say, 100, the brightness of the monitor does indeed change, but this is a less-than-ideal solution.

How can I fix this issue? I just want to control my brightness with FN + F7/F8 like I do in Windows 11.