Description

GTK 3 support is needed to run the Windows application installation wizard and CrossOver bottle management tool.  
This is not needed to run Windows applications.

Resolution

On CrossOver 17 and greater, the simplest solution to fix this issue is to run:

/path/to/cxoffice/bin/cxfix gir-data

Or add --show-all to see how CrossOver would fix it on your platform and others.

Alternatively you may try one of the commands below.

Arch Linux: pacman -Syu gtk3
Debian: apt-get install gir1.2-gtk-3.0 python3-gi-cairo
Fedora: yum install gtk3 python3-gobject
openSUSE: zypper install python3-cairo python3-gobject-Gdk typelib-1_0-Gtk-3_0

Notes:

• cxfix --show-all may have more up-to-date fixes.
• The commands usually also apply to derived distributions. So for instance a fix for Debian is typically also applicable to Ubuntu, Linux Mint, Deepin and Pop! OS. Similarly a fix for Fedora likely also works on Red Hat Enterprise Linux, CentOS, etc.