Providing a link of what you read will help us better understand what you’re asking.
I’m aware of no such dropping of flatpak support, EXCEPT that flatpak will not be available out of the box.
To use flatpaks in Lubuntu, just refer to the following doc
Lubuntu is one of the flavors that never provided flatpak support out of the box, thus no change occurred with us, though at least two flavors did provide such support in past releases but are now exactly where Lubuntu currently is.