Is it good to tell them
What do you want to do, and what can you do?
Do you have authority to change them and do you want to spend your time and experience on teaching them? What if they are angry and break the relationship?
If your answer is no, just pray and say nothing.
A private chat - where no one but you and the Christian you are referring to can see - is the best for small discrepancies, like “did you really mean you hate God?” obv. the person wrote the wrong word. That’s small.
For big mistakes, or what you see as big mistakes, a face to face private talk is best. Do it with love. See Matthew 18:15-17 for step by step instructions.
source:
Matthew 18:15-17 New King James Version (NKJV)
15 “Moreover if your brother sins against you, go and tell him his fault between you and him alone. If he hears you, you have gained your brother. 16 But if he will not hear, take with you one or two more, that ‘by the mouth of two or three witnesses every word may be established.’ 17 And if he refuses to hear them, tell it to the church. But if he refuses even to hear the church, let him be to you like a heathen and a tax collector.