When I print from Lightroom Classic to roll paper (on an Epson SC-P7500), I know how wide I want the print to be (usually 610mm). I have to estimate the height, then choose a "paper size" to match that height. I have a large number of defined paper sizes and presets so I can usually pick the right one, but it's a tedious chore.
In QImage One for Mac, I can select a box marked "auto roll length", and QImage will handle that chore, presumably by calculating the height and communicating it to the Epson driver.
It would be awfully nice to have a similar check box, with similar functionality, in Lightroom.