Steps to reproduce:
1) Go to Settings > Personalization > Colors
2) In the Choose your color dropdown menu, choose the Dark option.
3) Scroll down and uncheck Title bars and window borders.
You will see that the text of inactive tabs, as well as the add new tab, and three dot menu are all the same color as the title bar making them unreadable. This is with Groupy 1.21 on Windows 10 1903.