Operating system: Win10 Home 64
Graphics card: rtx3070

Blender Version
Broken: 2.93
Worked: N/A

https://cdn.discordapp.com/attachments/349254115567861762/826766151731773472/unknown.png

You must set Repeat to 2 or higher in the Smooth Stroke box in order to affect the Thickness. It should still average the thickness of the strokes at least a little bit when Repeat is set to 1, but as of 2.93 it is not affected at all.

The .blend file I included is ready for immediate use of the "Point > Smooth" function, just hit F3 and type in "point smooth" and hit enter, and keep repeating with Shift-R. You will see the locations of the vertices averaging, but not the thickness. Only setting Repeat higher than 1 will include Thickness in the smoothing.

Every time I single-use this function again, it resets the value of the Repeat slider to 1, although remembers if I changed the Factor slider to something other than .500

Exact steps for others to reproduce the error:

1. New file
2. Delete default cube
3. Add "Stroke" grease pencil object
4. Edit Mode on GP object
5. Select any consecutive vertices with varied stroke thickness, and use Smooth Stroke function ("Point > Smooth" in F3 Search)
6. Open the Smooth Stroke window and make sure Thickness is ticked