I have two textboxes in survey123
when number 100 is filled in first textbox
second textbox should auto populate with value "true", other then 100 the value is " false"
Take a look at the following documentation
Formulas—Survey123 for ArcGIS | ArcGIS
I'm thinking you'll want to setup a calculation like this in the calculation column of your evaluation question.
I have also attached an example XLSForm
Retrieving data ...