I have just installed SMath Studio 0.99.7030 on another computer and
added X-Y Plot Region Plugin using the Online Gallery.

Version of the plugin is 0.2.6961.xxxxx, while on the plugin page
version 0.2.7175.34428 (stable) is available.

unfortunately, I was unable to add the latter version using Online Gallery.

How to add X-Y Plot Region Plugin version 0.2.7175.34428 to my
SMath Studio installation?

You need SMath Studio 0.99.7109 from SMath Studio Versions History.

Thank you very much for your prompt reply.
I thought that the newest stable versions of plugins are loaded by the Plugin Manager.