Ever since the last update (v6.143), I am unable to open Group folders.
Double clicking on it does nothing.
I have tried restarting my Mac, quitting all other applications, but nothing helped.
Andreas: I can confirm that.
@BinaryBlitz10 Until the bug is fixed, activate “Folder Navigation Using Extra Columns” in the settings.
Unfortunately I was forced to migrate away from some old UI technology (storyboards) due to some bugs in the newer Xcode versions that make these impossible to use. That required a complete rewrite of the UI, which causes a few hiccups currently.
6.144 should fix various things and add the new Tahoe styling. It might look quite different than before on older macOS versions, I'll test with these older versions tomorrow.
6.144 has restored the old function. The rest... looks different.
It might also be quite broken right now, best go back to some 6.13x version for now
That's fine with me. The main difference is that the blue background in the leftmost column has disappeared. It is now gray 
although it is still displayed as blue.
v6.147 fixed it for me on macOS 26.2.0