Old question, “new” solution. On my 3k screen I can usehttps://github.com/kaueraal/run_scaledin order to get an usable Renoise window. Though this is admittedly less intrusive to desktop environments than the solution using xrandr (https://forum.renoise.com/t/dpi/30258), the update frequency of the spectrum pane is limited and not as fluent.
So for now I stick with the xrandr solution.