When I add or delete a file inside a project, I would expect that the project tree inside Gnome Builders sidebar reflect that change immediately, but that's not the case. I have to click on "Files" to reduce the content of the view to the root and click on "Files" a second to, to open up the tree and reload the folder contents. I reported the issue upstream [1], but I was told that Builder should behave like this. So this might be a problem within Arch Linux. I noticed the problem within Gnome Builder 3.32.4, but the same happens with Gnome Builder 3.34.0 from Testing. I attached a video to demonstrate the problem.

$ gnome-builder --version
GNOME Builder 3.34.0
$ LANG=C pacman -Qi gnome-builder
Name : gnome-builder
Version : 3.34.0-1
Description : An IDE for writing GNOME-based software
Architecture : x86_64
URL : https://wiki.gnome.org/Apps/Builder
Licenses : GPL3
Groups : gnome-extra
[...]
Installed Size : 40.47 MiB
Packager : Jan Alexander Steffens (heftig) <jan.steffens@gmail.com>
Build Date : Fri Sep 13 12:30:06 2019
Install Date : Wed Sep 18 14:56:34 2019
Install Reason : Explicitly installed
Install Script : No
Validated By : Signature

[1] https://gitlab.gnome.org/GNOME/gnome-builder/issues/1036