Hello and welcome to the forum!
I have found that you need to set AUTOUPDATER_Duplicati_SKIP_UPDATE=1 environment variable or realtime debugging doesn’t work.
I assume you’ve already cloned the git repo to your local machine. In VS, open the Duplicati.sln file. Set your startup project to Duplicati.GUI.TrayIcon and then just click Start. Note that when running in Debug mode Duplicati will place its databases in a different location so as not to interfere with Duplicati that may be installed on the local machine.
Hope this helps…