GTK2 apps don't support Wayland.
They should use the X server that is provided by XWayland.
1) Do you have installed XWayland? AFAIK Fedora split XWayland into its own standalone package.
2) Have you disable Xwayland on Sway?
3) Have you set the GDK_BACKEND environment variable? Forcing `GDK_BACKEND=wayland` in the environment is a bad idea.