This seems like the kind of question that should have been asked and answered over and over, but I can’t find the answer. I want the same folder to be accessible to multiple projects to use and edit. Copying the contents into every other project isn’t a good solution because then any edits I make in one project has to be copied out into the other projects.
I can kind of think of a way to do this with scripts, but it’s such an ugly method, and still requires maintenance because Unity likes to write its own solution and project files.
One way to do it would be using symlinks, but that would only work on a MAC / Linux. Basically what symlinks do is, they enable you to have one folder or file “appear” in multiple places, while having only one instance of it.
Another solution would be to use version control like git. You could setup a project on bitbucket, that would contain your desired folder with all of your assets (just the assets, not the entire unity project). Then you could clone that folder in every project that needed it. When you update something in any of your projects you could commit & push it to the repository and pull it on all of your other projects.
The best solution IMO would be an asset package. Have one project that has all of the resources you want to share, then just export them to a .unitypackage file. After that you can drag & drop it into all of your projects. But in this case you would have to update your base project & export the new package when you wanted to make a change…