Make sure the dopus.exe process is not running as administrator, as that will block things from the shell from being able to communicate with it. See here.
If it was not running as admin, could your antivirus be involved? Or any other shell extensions? Using ShellExView or Autoruns to check what else is installed, or Process Monitor to see which actions happen during the delay, may shine a light on what is happening.
I did some more investigation before, i even tried debugging which WINAPI Calls might be causing this.. but didn't work out.
It looks like when i click on button:
control.exe is spawned and it hangs for while (mentioned 5-6s)
When it finishes hanging, dopussrt.exe is spawned and control.exe is killed and replaced with something
I disabled all non-microsoft entries on shell extensions and left opus only result: delay present
I disabled all shell extensions, together with opus extensions: no delay.
Ok, it's Kaspersky Antivirus hooking engine causing problems with your ShellExecute hook.
When the kaspersky is fully uninstalled it works instantly, can you confirm this with your local kaspersky installation and notify them to fix this?
If one's using free AV software there is no reason to stick 100% with Kaspersky for good old times sake, or anything else in this sense. There are whole bunch of good solutions outthere and they should be checked before decision, through the sites like this: https://www.av-comparatives.org/comparatives-reviews/.
For example I run Bitdefender since it proved to be optimum in detection/performance and I bought it. If I'd noticed before that it does not support DOpus, I wouldn't bought it but would try other solutions as well. Right now I just need to wait until the license expires.