If your computer can do HDMI out, you can use a television as display.

In all seriousness, unless this is some kind of super-exotic situation (like, you’re on a sailboat in the middle of the Pacific and are suddenly needing to set up a Debian server) I would probably get an inexpensive USB keyboard to keep around. Even if you don’t normally need it (like, you use a laptop or something) there are a number of situations that it solves, like “one of my laptop keys has just stopped working” or “I actually need to work on some kind of computer that doesn’t have an integrated keyboard”.

kagis

https://www.amazon.com/sgmedila-Waterproof-Foldable-Flexible-Dustproof/dp/B0CXTHH7QS/

That’s not gonna be a very pleasant typing experience, but it’s under $4, if you’re determined to spend as little as possible.

Here’s a small, 640x480 USB/HDMI display under $50:

https://www.amazon.com/Capacitive-Compatible-Raspberry-Resolution-Interface/dp/B0CFJDTM5X/

I’d probably get a larger display, maybe used – I mean, maybe you think that you’re never gonna need to look at a computer’s output again, but you might find yourself troubleshooting a machine like this one, and 640x480 is a kind of significant limitation – but that’s at least a baseline.

If you specifically don’t want a keyboard, and if you have some other device with a display and text input and USB (well, or serial) support, I’d bet that the Debian installer can probably handle an RS-232 serial console install.

kagis

Yup.

https://p5r.uk/blog/2020/instaling-debian-over-serial-console.html

But I’m guessing that you don’t have the serial hardware. Having a USB-to-serial adapter is another thing that I keep one of around because every now and then I need to work on headless devices that have a serial interface, but I’ll concede that the serial port is getting pretty elderly.

I’d probably get a USB-to-serial male and USB-to-serial female adapter if neither end has an existing serial port (which these days, with desktop hardware, may be very possible).

Debian also has a fully-automated installer, as long as you can set your machine up to boot into it without a keyboard or display:

https://wiki.debian.org/FAI

That kind of thing is normally more used to set up VMs or manufacture hardware.

I would be very careful with that thing and probably wipe it after you use it, since it’s gonna be a USB key that wipes computers if you reboot and they’re set to boot off USB.

It almost certainly isn’t a great fit for your use case – like, the time you’re probably going to save setting it up isn’t going to be worth whatever you’d save spending on hardware – but mentioning it for completeness.