Good on you for sticking with it and trying to make it work.
I know you have already spent a lot of time on this, but it would be worth going through these same troubleshooting efforts (kernel parameters, scripts, etc) while using the LTS kernel instead of the 6.9.3 kernel. This is because it is possible the most recent kernel has introduced a regression.
sudo pacman -S linux-lts linux-lts-headers
You can boot to the LTS kernel by selecting it from the advanced options in the Grub menu, or make it the default boot option by adding the GRUB_TOP_LEVEL option in /etc/default/grub as described here: New Grub option GRUB_TOP_LEVEL
GRUB_TOP_LEVEL="/boot/vmlinuz-linux-lts"
As you must be aware from adding kernel parameters here, you need to regenerate the Grub configuration after making any changes to this file.
sudo update-grub