I am very new at trying to use the MI GRBL extension to produce Gcode files for a drawing robot. Here are the basic facts.

Inkscape version 1.0.1

MI GRBL Z axis servo controller    downloaded current version and added it into the extension folder.

Python ver 3.9

Using Win 10

When I select a drawing and then click on extensions, MI GRBL Z-axis servo controller I get the setup screen and then when I click on apply I get a new window that says 

Inkscape has received additional data from the script executed. The script did not return an error but this may indicate the results will not be as expected.

then below that

  File "servo.py", line 52
    def bezierslopeatt(((bx0,by0),(bx1,by1),(bx2,by2),(bx3,by3)),t):
                       ^
SyntaxError: invalid syntax

The Gcode file is not saved and I have no result from the action.

I am not a programmer but a user so I am unfamiliar with what this may mean. To me it means I cannot use inkscape for the purpose I want.

I have tried reloading all of the components several times and still get the same result. I even tried on a different computer running Win 7 with the appropriate Pyton and MI GRBL files.

Any help would be greatly appreciated.

I have the same problem. 
I saw it was possible to edit the file servo.py, but could not find the needed editing.

Here's what I did. Hope it works for you.

After many tries at fixing this I found the solution. It took reading the comments on thingiverse and following the suggestions offered in the comments, item 6 of the second update. Here are the details:

Python latest version 3.9 installed

Inkscape version 0.92.5X86

downloaded the version of MIgrbl suggested in the PDF instructions for the drawbot.

copied the 4 files in MIgrbl download to program files (86),inkscape,share,extensions

deleted the servo file from extensions

opened up the download for Draw+Robot+-+Arduino+Uno+++C

copied the servo file from the files folder

Pasted the new servo file into Program files (86),inkscape,share,extensions

Opened up Inkscape and all worked perfectly.

Thank you for the feedback. 
I have Python up to date, got a .92 (mac) version of Inkscape but it doesn't open on the latest mac OS, so I have to stick with version 1.01
I also did the updating of the servo file into the extensions folder. 

Unfortunately, the servo.py line 52 error remains

I found that with Inkscape 1.01 I could not get it to work. I am running Windows 10 and the older version loads ok. It really takes version .92. Maybe you could look on line to see how to get the earlier version of Inkscape to load on your Mac.

Unfortunately, earlier versions don't work with an updated mac os.
I did find a solution;
- from Inkscape 1, I save my svg
- and open it with jscut.org
- a few adjustments are needed with dpi (for overall physical size of drawing once gcode is generated), size of pen point for drawing instead of CNC, feed rates,...
- once gcode is generated, I only have to find / replace all the generated Z codes (vertical movements) with my servo codes.