[YaLTeR]

I will describe how PaperWM works; I think that behavior makes a lot of sense.

There are preset widths (by default: ~33%, 50%, ~67%) which you can toggle between with a key, plus a 100% "maximized" width that you can toggle separately. This works out pretty well from my experience and gives you the convenient 33/67 and 50/50 layouts (or 33/33/33 on ultrawides).

The initial window width is what the window wants. So the window is free to use any size on creation, then PaperWM expands it to full height with the same width that the window had selected.