I know there has been discussion on this, however, I still struggled for a day when I was trying to install Zwift on my PC with Win10 system. Hence I would like detail below with you.
I experienced the issue that Zwift does not have access to “user/user/Documents/Zwift” folder. After trying all suggestion in previous posts, I still failed to address the issue.
I looked at the issue further and here is what I found.
When you install windows 10, if you did not turn off Onedrive backing up your documents, it could potentially move your “Documents” folder to “user/yourusername/Onedrive/Documents”
When we talk about “Documents/Zwift” folder, it is important to tell the difference between relative path and actual path. In window10, when you click on “Documents” in your file explore, you are using the relative path, but specifically, for Zwift to work, you need to make sure it is your access to the actual path of “C:\user\yourusername\Documents” and make sure the relative path is set to this for your “Documents” folder.
The relative path of “Documents” can be changed, what you need to do is to right click on the “Documents” line in your quick access section and choose “properties”, then there is a tab called “location”, then choose “restore default” and apply. You might have issues doing this if it is clashing with Onedrive setup, so depends what you need you might want to google how to do it. For me, I had to uninstall Onedrive, then use a registry edit entry I found online to restore the default setting. Then you can copy all stuff in your old “Documents” folder on Onerive path to the default “C:\user\yourusername\Documents”.
When you install Zwift, it would install all package to “C:\programes(x86)\Zwift” unless you change it, but at the same time, it would create a folder called Zwift in Documents to store logs and workout history. So if you finish installing Zwift not even seeing the subfolder in “Documents”, it means it for sure would fail.
The whole issue is really an issue of no issue to be honest, all Zwift need to offer to people is ability to specify two paths in installation process, one for the software ( namely "C:\programes(x86)\Zwift), another for logs and personal data. Even if Zwift want to hard code the logic to force user to save all the logs and workout details in “Documents”, it obvious has done done it properly as other applications. Without going into details, I do have other applications installed on my PC, some big some small, but none of it had issue dealing with the relative path of “Documents” or synching issue of Onedrive.
Hope it helps in case you see that annoying “error accessing writable storage” when you trying to use Zwift.