File share / mapping - how to do this?

I intend to share the cryptomator vault locally. but for some reasons I cannot change the required attributes.
Does anyone know how to share a vault?

Reason: I use two computers and one shall be the encrypted backup of the other computer.

I am not sure what you mean with “share” and “required attributes”.
But if you want to transfer a local vault from one PC to another, you have to set up a sync process for the encrypted vault files (the folder where the masterkey file is stored) or copy the encrypted vault files from PC 1 to PC 2.
As soon as the encrypted vault files are local available on PC 2 and cryptomator is installed, you can add this vault to cryptomator and open it with your password.

Thank you. :-). The issue is the following: I cannot grant shared access of the vault to any user on the same computer or on the same LAN. This is because when I try to change properties of the vault (which in my case has drive letter d:) I cannot change the properties regarding sharing - any other directory can shared without problem but not the vault. When I change the properties and try to save a message appears that I cannot save the changes.

Thus I can neither copy nor robocopy nor sync the vault from one PC to another PC.

Is there a way to overcome this?

You are trying to grant access to other users to the content of your vault.
The content is shown as a virtual drive. You cant share virtual drives as far as I know.
If you want other users to have access to your files inside your vault, try mounting the vault as folder and not as virtual drive. To do that change your volume type in the app settings to WinFSP (local drive) - assuming you are on windows - and then configure an empty folder as mount point in your vault options.