For a US government job that requires a security clearance, tell the truth for every question they ask you, but you do not have to volunteer additional information.
As a Federal employee for 30 years, keep in mind that the fist year is probationary, you can be dismissed for any cause, not matter how slight, but it must be a real issue, not a fabricated issue. The next two years you are a conditional career employee. You can still be dismissed for cause, but it requires a more serious offense. After 3 full years of satisfactory work, you are a career employee and any dismissal requires a hearing before dismissal, which can be appealed. To fire a Federal career employee is almost unheard of, but I have seen it with someone who repeatedly violates the conditions of employment.
Being transgender is currently not a cause for dismissal. Your supervisor may have issues with it, but they are always stopped during the appeal process.