Is it safe to delete .nuget folder inside my user profile folder?

Yes, the .nuget folder is used as a cache for packages downloaded to speed up project restore and compilation. It can safely be removed. Worst case, it will have to download the packages again in the future.

Just to follow up on the answer @jessehouwing gave, here is the official documentation explaining the different package folders and how to manage them via supported tooling: https://docs.microsoft.com/en-us/nuget/consume-packages/managing-the-global-packages-and-cache-folders