This fork of the main rosserial package fixes some issues with how Ethernet communication is handled on the Teensy 4.1. To install into ROS, you need to build this package rather than installing the binaries directly from the ROS Package Manager.
Where is the Catkin workspace you want to install into:
cd <ws>/src
git clone https://github.com/CU-Hyperloop/rosserial.git
cd <ws>
catkin_make
catkin_make install
Please see rosserial on the ROS wiki to get started.