How to 'extract' a .vsix file? (i.e. not install)

Rename the file extension to .zip and voila, just unpack it like a regular zip

You can download vsix file 2way. But vsix file downloaded by first site can't extract linux unizp. you need to download second site.

first one

https://marketplace.visualstudio.com/_apis/public/gallery/publishers/${publisher}/vsextensions/${extensionname}/${version}/vspackage

second one

https://${publisher}.gallery.vsassets.io/_apis/public/gallery/publisher/${publisher}/extension/${extensionname}/${version}/assetbyname/Microsoft.VisualStudio.Services.VSIXPackage

If CSS Peak

${publisher} = pranaygp

${extensionname} = vscode-css-peek

${version} = 3.0.2