A family of Microsoft relational database management systems designed for ease of use.
Installing the Runtime license can interfere with an installed version by grabbing the association with the accdb file extension and opening all files in the Runtime. That's why its best to install the Runtime in a VM.
However, its not necessary to even install the Runtime on a machine that is used for development You referred to the accdr file extension. That is not something created by Access. An accdr is created simply by renaming an accdb as accdr. When a full Access installation opens an accdr file it acts like it is a runtime version. So if you want to test how your app will work in a runtime environment. You can just rename it as accdr. Name it back to accdb and you can open it with full access to design elements.
Note also that a machine with only the Runtime installed. does not require an accdr extension. It can open accdb and accde as well ac accdr.