The .iso gets written. like the .iso files of yore being burned as an image to CD or DVD. (Also like the .cue files where, in your optical media burning software would be written with something like 'burn as an image' or 'burn image' or 'write image' or similar, depending on the software.)
It's the same thing - though you can 'write' an .iso to a USB with tools like Balena Etcher.
You don't just extract the .iso and boot to it. That doesn't work. It has to be written as an image file to the device, be it CD, DVD, or USB.
So, can your server boot to USB and can you attach keyboard and monitor temporarily?