rdpweb/webclient3.html not work becouse SWFObject 2.2 no longer works properly. The bug in SWFObject has already been reported on GitHub, but the library is unmaintained.
The new “HTML by default” Flash policy starting at Chrome 55 does not initialize the variables that SWFObject uses to detect whether Flash is installed. Specifically, navigator.mimeTypes no longer contains application/x-shockwave-flash, unless Flash is enabled by the user. Other browsers have similar issues related to the click-to-run activation scheme introduced as part of Flash’es end of life.

May be try alternative client? Example https://github.com/cedrozor/myrtille

I found this article: https://stackoverflow.com/questions/40880942/swfobject-embedswf-not-working