Hello,
Sorry to hear you are having issues.
I was able to add tabs with file selected . running Windows 10 Groupy 1.17

What version of Windows and Groupy you running?
I would try a Purge https://forums.stardock.com/488142/groupy-support-faq#reinstalling
then ReBoot and Reinstall , then report back here , please.
AzDude
Stardock Community Assistant