This resizable Quick Settings tiles feature seems to be part of the overhauled Quick Settings panel that Google is working on for Android 16.

Last month, we reported that Google is working on a major overhaul of Android's Quick Settings panel for next year's Android 16 update. From what we managed to enable, it looks like Google wants Android to show more notifications and Quick Settings tiles on screen, and the best way to do that is to split the notifications and Quick Settings panels into two separate pages. However, there's another way to fit more Quick Settings tiles on screen, and that's by making them resizable, which is something that Google is seemingly working on for Android 16.