In order to get TrueRNGpro to work in Linux (Ubuntu 21.04), I had to modify the /etc/udev/rules.d/99-TrueRNG.rules file such that:
1. The product, idProduct and idVendor matched the results from lsusb -v
2. Remove the line break between the lines
# ubld.it TrueRNG
#
# This rule creates a symlin to newly attached CDC-ACM device
# Also includes fix for wrong termios settings on some linux kernels
# New! includes ignore for modemmanger
# (Thanks neoaeon)
SUBSYSTEM=="tty", ATTRS{product}=="TrueRNGpro", SYMLINK+="TrueRNG", RUN+="/bin/stty raw -echo -ixoff -F /dev/%k speed 3000000", ATTRS{idVendor}=="16d0", ATTRS{idProduct}=="0aa0"
.
