[SOLVED] Regression in Thunderbolt connected eGPU functionality between 6.8.4-2-pve and 6.8.12-4-pve

[scyto]

what file should this appear in?

you have it in the right file, just not on the right command line, it should be in the GRUB_CMDLINE_LINUX_DEFAULT= paramater after quiet and remeber to run udate-grub afterwards and update the initramfs too