Hi,
I have added an environment variable of boolean type in both parameters as well environment section.
For the parameter section I am setting its default value as true using parameter.value. Because of that it is showing as checked.
And same I am trying to do in the environment section by setting the value like arcpy.env.transferDomains = True. It is setting the value but not showing the checkbox as Checked.
Added the screenshot where transferDomains checkbox is not checked when tool is opened for the first time.
@EarlMedina @JoshuaBixby