Install with custom firmware

Some hardware device firmware is often too old in the Debian stable distribution to allow the installation to complete, particularly for NICs required during a network install.

The installer looks in /lib/firmware, so we'll need to make sure the necessary files are here ahead of time.

Download appropriate firmware package, use backports for devices not supported by stable.

Extract the firmware directory:

ar x firmware-realtek_20210315-2_bpo10+1_all.deb
tar xf data.tar.xz
cp lib/firmware/* /media/$USER/$DISK

Then at the installer, plug in the device, mount the partition at /lib/firmware:

mkdir /lib/firmware
mount /dev/sdb1 /lib/firmware