I assume, since you use the terminology "polyline" that you are in the Fusion page of Resolve. Furthermore, since you say "radius handler," I assume you're asking about controlling the softness of a double polyline shape, and not talking about manipulating the normal bezier curvature handles. Also, to be clear, Fusion polylines behave differently than the power windows found elsewhere in the Resolve interface.
One method of controling Fusion double polylines:
- First, activate Double polyline by clicking the outlined "D" icon if you haven't already.
- Select all points with Shift-A
- Hold the "O" (offset) key and click-drag in the viewer.
There are other ways to control double polylines. More information can be found in the DaVinci Resolve user manual. As of version 16.2, the relevant pages start at 1298.
Key bindings in Resolve's Fusion are customizable, but not out of the box. If you're determined to change them, the simplest way would be to use stand alone Fusion, which has a built-in hotkey manager in the "Views" context menu. The compositions you create in standalone Fusion are easy to copy-paste into Resolve Fusion (but know the difference between Loaders and MediaIn nodes; Savers and MeidaOut nodes).
Alternatively, you can install the Fusion plugin package manager, "Reactor," which is available here, and install Andrew Hazelden's "Resolve Essentials" atom, which includes a script to edit Resolve Fusion keybindings. Personally, I'd leave them alone, though.