If you find an extension that you would like to add to Inkscape 1.1  and the files are on Github.com, here's a brief look at how to do that.

1. Go to the project on Github.  Click on the button labeled "Code" .  It will give you the option to download the zip.

2. Unzip the downloaded file

3. You will see the extension files there -- they have  a suffix of  .py and .inx

4.  Copy these files to your Inkscape extension directory.   It will be something like this (but substitute your system username for username)


5. Close Inkscape if it is running, then restart.  Your extension shoul be available at this point. 


Here is  where the button is on Github for the Extruder extension, for instance.