All my Non Muslims friend, Please don't take this topic as offending or hateful towards you - You have got every right to celebrate your occassions but I just want to share some useful information with my fellow muslim brothers and sisters.
AOA brothers and sisters,
There is a masla, Can we can say Happy diwali, Happy Diwali to our non muslim friends/colleagues, now I am not trying to tell you my opinion, but want to share some useful information regarding this masla
A Muslim can however greet and compliment a non Muslim on matters not concerning religion they follow, such as winning a sport, passing an exam, on getting promotion in job and so on.
Allah knows best and may kindly forgive me for any error.