Is the LabQuest screen bright enough for outdoor use?

Yes. The LabQuest screen is bright enough for fieldwork, even at 75% (default) battery level. For an even brighter screen, you can choose Power & Light from the Control Panel and increase the brightness to 100%.

LabQuest 2 also has a high-contrast mode for better viewing in sunlight. To activate high-contrast mode, got to:

Home / Preferences / Light & Power

Check the option for "High Contrast", and the screen will be easier to view outdoors.