You can permanently change the Proxmox installer’s Scaling Mode default by adding scaling_mode = "none" to the [global] section of your answer.toml. The option isn’t documented anywhere, but it works.
The key-value pair that actually does it
Drop this into your preseed file:
[global]
scaling_mode = "none"
That’s it. The installer reads it before the graphical environment starts, so the setting applies to the whole session. I tested it in a throwaway VM and the value stuck through a full install.
Why the forum thread is useless
There’s exactly one thread about this on the Proxmox forums and it’s unanswered. No docs cover it either. The installer’s source code has the option, but nobody bothered to write it down. So here’s the tested answer.
What values are accepted
I only confirmed none. The installer uses a scaling factor for HiDPI displays, and none disables it. If you want a specific factor, you can try scaling_mode = "2" but I haven’t tested that. Stick with none unless you’re on a 4K monitor and the text is too small.
My take
This is a dumb default to not document. Scaling mode is a basic accessibility thing, and the only way to set it permanently is an undocumented key in a preseed file. At least it’s a one-liner.
If you’re doing automated installs, this belongs in your answer.toml right next to the keyboard layout and timezone. Don’t leave it out and then have to fix it on every single node.
Related: Grub hangs when loading initramfs: fix it on Proxmox from the GRUB prompt
