Hi, I am Phil, the guy that designed and sells the grblHAL board Jonas and Chris are using. Happy to answer any questions - especially about custom builds.
I was able to connect LB to a grblHAL board by going into devices, Create Manually and selecting GRBL (not LPC or M3). Then selected USB (only option, will be posting a question about that later) and it just works.
The key to getting higher speed is a custom build that increases the motion planning buffer to 1024. The Teensy 4.1 used on the breakout board has a huge amount of RAM, unlike some of the other processors that various GRBL ports run on. I will be doing a short blog post on how to set this up soon and will post a link here when I am done.