PaperWM has columns - you can move multiple windows into a column (Super+I by default, or Super+O to move a window out of a column). When you move windows left or right or resize horizontally the column moves or resizes as a group. That’s the only feature that groups windows.

I mention Niri because I’m interested to see more implementations of the same idea. The only other scrolling window manager I know of is CardboardWM which is long dead. A native implementation like Niri might be able to explore ideas that are difficult to implement in an extension.