If you use Fedora, CentOS, or a SuSE/OpenSuSE variant, there are a few things to take into account to get the Xojo environment running. Since all three default to KDE/QT as the desktop environment (unless you download a custom GNOME/GTK version), there are some things that you will need to do BEFORE trying to run the IDE. Also, do not bother with the DEB/RPM packages and just get the TGZ Xojo package.
Download the Xojo TGZ package to your Downloads folder and do this in a Terminal:
sudo -s yum -y install gtk3 gtk3-devel libunwind cd /opt mkdir xojo cd xojo tar -zxvf ~/Downloads/xojo2018r4.tgz
Next, add this file to /usr/share/applications/:
You still need to use sudo to add any plugins to the resulting install in /opt/xojo/xojo2018/Plugins.
You're now there based on my experience with CentOS 7.5.