Curve/envelop deformer with a straight object?

Has anyone tried applying either of those to something like a cube or any other straight object?

It seems whenever I try, if i pull the handles out it will require the object to be a curve, and if i leave it in default mode where it looks like a line, once i start deforming artifacts of the object appear quite fast.

click=bone mode
pull=curve mode

Loong

Yeah I tried clicking but like, if I move it towards center the fill starts to spill out on the sides.

Post a screenshot, it will help to see what’s happening.