Problem
When you run Fedora 38 XFCE Live image and click on Install to Hard Drive, a dialog pops up, claiming that this launcher is untrusted:
Cause
A change in the XFCE security model requires launchers to be marked as trusted. This change was implemented too late in the XFCE live image and didn’t make it into the Fedora 38 final release. It will get fixed in Fedora 39 install media.
Related Issues
Bugzilla report: #2172854
Workarounds
Simply click Launch Anyway and the installer will run. There is no security risk, because you’ve downloaded (and trusting) the whole Fedora XFCE image, and the installer launcher is just a small and negligible part of that.