Comment 54 for bug 1652282

This is a known limitation and design choice that Wayland doesn't allow
root privileged applications to work.

One workaround is to run the following in a terminal before running
GParted to allow root applications to connect to the X server under
Wayland.
  xhost +si:localuser:root

Another workaround it to continue to use the X.org display server rather
than the Wayland display server.

More information can be found in the:
  Common Fedora 25 Bugs / Running graphical apps with root privileges
  (e.g. gparted) does not work on Wayland
  https://fedoraproject.org/wiki/Common_F25_bugs#wayland-root-apps