The dictionary said Ne also means 'about him' but when I wrote 'We talk about him later' it said it was a mistake

In English iit is correct to use 'shall' for the first person singular and plural of the future of 'to be' (I shall you will he will she will, We shall you will they will0, Then the reverse for expressing strong determination.

I did the same thing and also got a mistake. I think it should be accepted as both about him and about it are valid. If it is not valid in a certain sentence, I don't think it should show as a possibility. The full list of possible meanings will be in the vocab. or become clear with other sentences.