I recently cleaned up my previous installs of RT so I can’t trace the past history. However originally I did indeed get gdbus via How do I switch from edit window to browser window? - #30 by gaaned92. That was for RT 5.8. But I don’t recall worrying about it subsequently through 5.9 and several development versions. It may well be that in fact I copied it from install to install when copying over profiles and configuration files etc. But I have no recollection of doing so and the configuration profiles are in my local app directory, not with the RT executable. So basically I don’t know, except that originally I got it externally.
However, regardless of the details of the past history, it seems reasonable that gdbus should be included in the windows installation package so that the -R option works; or if for some reason it is not appropriate to include it in the installation package, it should be documented in rawpedia.
If you think it appropriate, I can write a bug report on GitHub.