I had problems with all the file|open dialog windows in Shotcut, the video editing application. I would get an empty window instead of a file chooser and the application would hang with a GtkDialog error in its log, followed by other gtk errors.
I am running openbsd 6.8 with fvwm, and had installed shotcut-20.07.11 using pkg_add. I was able to fix this by installing the qt5ct package and setting the environment variable QT_QPA_PLATFORMTHEME to "qt5ct". I got the idea for this fix from someone who appears to have had the same gtk errors in a different application also running on openbsd, https://github.com/qgis/QGIS/issues/25720 I'm not knowledgeable enough to troubleshoot this further, but thought to pass this fix along in case it might help anyone else. Mike
