Running xfce desktop for a long while, by guessing, 1day or longer, with or
without suspend/wakeup.

Launch xfce4-screenshooter, capture whatever region, at whatever dalay,
then select `Copy to the clipboard`, click OK. Clipboard has no image. but
/tmp/ has a newly created `Screenshot_<date>_<time>.png`

It seems that the bug may be in the xfsettingsd process, which eventually
stops copying images for reasons that are unclear.

workarounds might involve using clipman or killing & restarting
xfsettingsd. It might also be fixed upstream in a new version, which also
consolidates the clipboard code into libxfce4ui, shared between clipman &
xfsettingsd.

https://bbs.archlinux.org/viewtopic.php?id=294394&p=2

https://gitlab.xfce.org/xfce/libxfce4ui/-/merge_requests/117