Windows don't follow split-width-threshold

[mgsb]

I use split-width-threshold to break a frame into multiple columns for windows. Opening a new popper window does not "split" like other windows so it ends up spanning the whole frame. Is there a way to make new popper windows split like "normal" windows?

[karthink]

Yes, you can use a different popper-display-function, OR turn off Popper's window handling entirely (set popper-display-control to nil or user) and customize display-buffer-alist.

For the former option, you want a display-buffer action that does not use a side window. (Side windows cannot be split.) For example, you could try display-buffer-below-selected or display-buffer-in-direction.