I've read about this problem elsewhere, but still can't make it work. The influence circle is apparently too large to be visible and the scroll button only has a regular zoom effect on the scene. Scrolling out doesn't help. Tried scaling up the object, and still nothing. Tried opening a fresh scene with the default cube with same result. I was able to use prop. editing once in a tutorial, but never since then. Using 2.82.7. Any suggestions?

Try this to see if it helps. Turn proportional editing on. Go into edit mode and select a vertices. Press the "G" key and then immediately press the left mouse button . A dialog box should have opened at the bottom left of your screen. In the "Proportional Size" field enter 1.0. Now press the "G" key and you should see the circle of the proportional editing tool on screen. This should work if the problem was that the tool size setting was so high that scrolling didn't help.

I noticed that you will not see the Proportional Editing radius if you are using tools like Move, Rotate, or Scale from the left side Icon panel. Those tools enable the Gizmo, but the Proportional Editing radius isn't visible and the scroll wheel will only engage the zoom. So, if you try what Keppel suggests, press G, then you can use the scroll wheel for the proportional radius adjustment. You can see the proportional size text in the upper left-hand corner of the workspace on a default Blender layout, so you can see what size the proportions are at. And, as Keppel suggests, you can also use the tool panel popup to adjust the proportional size, but this still won't show the radius circle if you pick a tool from the icon menu bar at the left. I'm using 2.81, but the same is probably true for 2.82.

This seems to work! Thank you both!