CrossOver no longer uses GTK 2. This article left in place for reference only.

Description

GTK 2 support is needed to run the Windows application installation wizard and CrossOver bottle management tool.
This is not needed to run Windows applications.

Resolution

CrossOver no longer uses GTK 2. See the Missing Python 3 GTK 3 support page.

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

/path/to/cxoffice/bin/cxfix gtk2

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.
Debian : apt-get install python-gtk2
Fedora : yum install pygtk2
openSUSE : zypper install python-gtk

Notes:

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