At first unrelated to this, I followed your advice in another thread on how to install the extension “Data Wrangler” on cursor (i.e., manually via VSIX). This worked, but I didn’t have the Jupyter extensions installed, so Data Wrangler did nothing, but I suddenly had the icon again.
After the next Cursor update/restart, Cursor asked me whether I wanted to install the Jupyter stuff. After doing so the test icon was gone again. 
Does anybody have a good recommendation for a safe extension that does nothing and doesn’t work? Maybe that’d fix the problem. 