GStreamer OpenGL plugins cause windows to be listed (wayland)
I guess this might well be a wayland/xwayland issue, but when I run the following pipeline
gst-launch-1.0 videotestsrc ! glupload ! glcolorconvert ! gldownload ! ximagesink
then I get two windows listed in the Alt+Tab dialog. One "GStreamer" window which is the display and one "Unknown" window. This "Unknown" window seems to be related to the GL pipeline elements.