For anyone not yet aware, Graphiisoft's developer site has a web app to assign developer MDID's for your Addons. This app functions much the same as the Addonadmin.exe program as was previously used to create Addon IDs.
In addition to creating new IDs, you can also download your existing XML files and now keep all your IDs on line. The app seems to be much easier to use and understand. It removes the necessity of using the Addonadmin program which seemed to contain a new bug every year. This looks to be much more useful -- check it out.
Tibor made a good instructional Blog which describes its use. The app is listed under your Profile Settings.
Windows 10 - Visual Studio 2019; ArchiCAD 26