It seems that the height of bubble mode is restricted to something like half the screen. Makes it hard to see the whole conversation. It fits the keyboard expanded perfectly.
If possible, it would be better if wechat bubble can expand to the full screen like other apps, and change dimension when you open keyboard. Don't know if that's possible or not. I know the feature is experimental, probably you already have plans to do this, and I guess this issue is kinda just a self-note
Using pixel 2 xl, version 6.2, Android 11, wechat 8.0.1, and gboard