[Scale] can make things larger or smaller, but cannot be used  to create text outlines.  This is what [inset], [outset], [dynamic offset] and [linked offset] are for.

[Inset] creates an outline that is smaller than the original.

[Outset] creates an outline that is larger than the original.

Both [Inset] and [Outset] produce a path by converting the source object to a path first.  There are no handles.  You would have to clone the source object first if you want to keep it.

[Dynamic offset] is more intelligent.  It creates a handle you can drag to make the offset larger or smaller.  However this operation also converts the source object to a path first.

[Linked offset] does the same as [Dynamic offset] and provides a handle.  It also creates a copy linked to the original shape.

Long story short: just use [Linked offset].

Problem #1

Handle does not appear.

Cause

You either converted the offset to a path, or you converted the linked source object to a path.  If you convert a linked offset to a Path object, you will no longer be able to modify the radius as it is now a ‘flat’ path shape object.  There is no ‘radius’ parameter any more.  There is no handle.  It is just a plain shape.

[Linked offset] works great on Text shapes.  If you convert the linked Text shape to a Path object, the linked offset shape can no longer be adjusted you just converted the object it was linked to.

Solution

Don’t convert a [linked offset] object nor the object it is linked to.

Problem #2

When I apply a [linked offset] nothing happens.

Cause

You can double click to enter a grouped object.  Make sure you are not inside a grouped object by simply double clicking outside of the grouped object to ‘exit’ the grouped object.
Also, sometimes you have to ungroup (text) shapes before linked offsets can be applied.

Solution
I find it easiest to apply a [linked offset] and just check the status bar at the bottom to see if an offset was applied.
Rather than looking for a handle that may or may not appear I then simply modify the radius as follows:

Inkscape does not yet have a GUI option to numerically input and modify the size of the offset.
You can easily adjust the offset numerically using the built-in XML Editor:

Select the dynamic offset
Open menu ‘Edit > XML Editor…’
Change the value of the attribute ‘inkscape:radius’ to the desired number of px

Inkscape Advanced Tutorial

For an advanced quick user guide, visit the following web site:
https://inkscape.org/en/doc/advanced/tutorial-advanced.html