Not sure if this is the current expected behaviour but I can’t seem to get the frame rate limit to work at all, the Legion Go tries to run 144 fps all the time, unless the game engine is locked to 60 or I reduce the TDP down low enough for the frame rate to drop, which results in very poor usability.
The screen seems to really chew up the battery at 144hz, would love to be able to lock it down to a lower frequency, I also cant seem to find a way to reduce the screens resolution in Steam Game mode either, would be nice to reduce that as well, as even the Steam interface chews up battery at an alarming rate.
You could also choose the global option in the first picture shown lower left corner. That will enable for all games and even some apps which can be problematic unless you set some other things also.
For starting out I would just use the launch option.