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