nnimap gmail "A T" and "^" not working

[JibStyle]

Hi, I am new Gnuser coming from Gmail web interface. I have mostly
configured my nnimap server for gmail and I see it has great power!

Unfortunately, I am unable to get "A T" and "^" to work in the nnimap
summary buffer. I would like to reconstruct threads, and some articles
may be in another group. Even if they are in same group, "A T" only gets
parents but not siblings or children. I have spent days trying the
various configurations cited in `(gnus) Finding the Parent' info page to
no avail.

Does anyone have any tips? What is your configuration for nnimap gmail
threading?