Hello,
When we join a team, all our local data (workspace and collection) is lost.
While
… In Microsoft culture, when we install new Windows, the data and files of old Windows are kept.
Please pay attention to this big mistake in your culture.
Could you elaborate more on this issue please? There’s no a lot of detailed here to help us understand what might have happened. Did you previously have account before joining a team?
The more context that you can provide, the easier it will be to help here. 
Thank you Danny .
when i use postman without singing to any account . means i work in offline mode
when i create collectionas and workspace in this mode …
after that , when i want tol ogin to my account or join a team
all of local collections that i made before in offline mode. will be lost
testing this situation is simple .
logout from your postman in desktop app . then create a workspace .
after that login again . you will see what happend for your offline collection .
Which version of the Desktop app are you referring to here?
You can’t create Workspaces and Collections without signing into an account. You can build requests and send these to test your APIs but these are not saved into a Collection.
If you were then to sign into an account, you would see this option:
In this case, I have created a new Workspace and the request that I made while signed out, is open in the workbench are in the History section:
Can you share a recording of the behavior that you see, if you’re seeing something different?