And no, by the way, I have no other computer with
which to get on the
internet, and never use my phone for internet. Someday perhaps I will get
another machine, but at present I have about six more machines packed away
in storage.
If I were you, I would install Debian/Devuan on USB stick. You can instruct
the BIOS to boot from USB if available, in some cases even from specific
USB Stick. This way you will not put your work environment in danger.
When this works you can transfer the installation to the disk or install on
the disk.
In any case a bootable USB drive is very useful tool to have around.