Is this correct form by English grammar: “After then, that I came home, I ate.”?

After that, i came home and had food.

I think what you’re trying to say is “Afterwards, when I came home, I ate” What language do you speak? If you say it in your own language someone might be able to translate better for you.

We don’t say “after then.”

We might say “After that (happened), ….”

We could say, “After that, then I came home and ate.”
The trouble with this sentence is that “then” and “after that” pretty much mean the same thing. So it’s a little repetitive to use both in one sentence.

You might use them both for emphasis –
“No, no, I tell you! AFTER that — THEN I came home and ate — not before!”

The best way to phrase the idea is
“After that, I came home and ate.”
-or-
“Then I came home and ate.”