Yes, you are right. Problems occur at a baud rate of 2 Mbps, and this not only affects the connection with LN-101, but also with U2D2.
Unfortunately, I do not have access to Portenta H7, OpenRB-150, RPI-4B or Jetson Nano. Especially with Portenta H7, RPI-4B and Jetson Nano I am not sure how I could connect them to my openManipulator-x as they don’t seem to have a TTL interface.
As for OpenRB-150, I tried twice and it was defective both times, so I am rather reluctant to try again. (see my forum post for more information)