I need to share desktop via Spark or some other client connected on Openfire server,
could someone help me to do this.
Spark doesn't have such feature. I see that Jitsi has an option to share full screen or a region, but you probably have to use Jitsi on both ends for this to work (shows me blank menu entries, becausei have Jitsi only on my PC). https://jitsi.org/
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