I know this can be done because I managed to get it set up on a previous laptop. However that has unfortunately died and I’m now trying to get myself set up on my new machine but can’t for the life of me remember how I managed to set up generative design with Dynamo Sandbox. 
I’ve tried searching here but couldn’t find any info which has really confused me as I’m sure I got the info from here in the first place!?! Could someone please put me out of my misery (@JacobSmall?) - thanks 
You are looking for the Generative Design view extension in Dynamo sandbox, yes?
The way I like to use is to copy the extension from:
C:\ProgramData\Autodesk\RVT 2021\Dynamo\2.6\packages
to your Dynamo sandbox package location:
ex: C:\Users\%USERNAME%\AppData\Roaming\Dynamo\Dynamo Core\2.10\packages
The other method is to add the following directory to your list of node and package paths: C:\ProgramData\Autodesk\RVT 2021\Dynamo\2.6\packages
This is perhaps less stable in the long term due to the potential of an update to Revit 2021 or an update to Generative Design for Revit changing that path to C:\ProgramData\Autodesk\RVT 2021\Dynamo\<ValueLargerThan2.6>\packages, but that won’t be an issue for at least 3 months (hopefully that reads as coping the contents as @john_pierson pointed out being my preferred method at the time of writing).
That is one of the reasons I didn’t mention the mapping.
The other is, Dynamo requires packages in ProgramData to be signed with a security certificate. So there is a chance that you “map” to that location, install some new packages, and they mistakingly go in there. This would result in pretty much every community package provided not loading as I don’t know of anyone signing Dynamo packages. (I actually do have the ability to sign my DLLs for Rhythm, Bang, and Monocle, but I elected not to as it isn’t required for AppData package locations).
I tend to leave package paths alone all the time and copy what I need to the built-in location. More often than not, adding or moving package paths causes issues.
I remap all the time to put myself into an environment which aligns to that of whoever I’m working with, and yeah there can be issues (usually around trying to use the old version of the package after a Revit update causes a dependency conflict with CEF or similar, or accidentally giving two versions of the same package causing nothing to load because I failed to manage things). To date I haven’t seen stuff install to the program data folder yet though, but it’s a good thing to note and keep an eye out for.
