Adding file name extension in the Export dialog
In the "Export" dialog ("Export this version..." command), if the user forgets to add the ".zip" extension to the file name, they end up with an extension-less file name. Similarly, if they insert another extension (i.e. something different from ".zip"), they end up with a misleading name. I'd suggest that TortoiseGit add ".zip" to the file name if it does not already end with that.
What version of TortoiseGit and Git are you using? On what operating system?
TortoiseGit version 220.127.116.11 Git version 2.16.2.windows.1 Microsoft Windows 10 Pro version 1803