Running a freshly installed Raspberry Pi OS Desktop on a Raspberry Pi 4, I'm trying to install software using the graphical Add/Remove Software tool. For example, Visual Studio Code. After checking the tick near the code entry, I clicked OK. A popup appears that additional confirmations are needed because other software has to be changed:

I confirmed with Weiter (which means continue) but nothing happens. The list appears again and it seems that nothing is working on installing the software, there is no CPU/Network/IO usage.

This doesn't change after waiting for a few minutes. The code command is also still not avaliable.

Using sudo apt install code on the commandline works, about a minute later VS Code is avaliable using the code binary as well as in the application menu of the pixel desktop:

The same happens on other packages like vim: The GUI doesn't do anything, installing using the terminal works perfectly. I tried to run the Add/Remove software gui using the pi-packages command from the terminal, in hope to get some information, but I only get the following lines immediately after startup (without doing anything in the UI):

$ pi-packages

(pi-packages:5577): Gtk-CRITICAL **: 16:11:10.005: gtk_widget_get_style_context: assertion 'GTK_IS_WIDGET (widget)' failed

(pi-packages:5577): Gtk-CRITICAL **: 16:11:10.005: gtk_style_context_add_class: assertion 'GTK_IS_STYLE_CONTEXT (context)' failed

Why is the GUI not working? What's the problem?