Private mode not working

[Android Central Question]

I have checked on root checker and got that my phone is not rooted but while turning on the secret mode in internet browser on my galaxy s6 it tells that rooting detected in my phone even i have reset my phone many times plz plz plz help me!!!!! And tell me can i install any custom rom on my G920W8VLU5CPK4 galaxy s6 device?????
help me can i install custom rom of G920W8
Plz tell me !!!!!