Your setup seems to be that the windows server has a Samba volume that is mounted on the Linux client. On the Linux client you use restic to mount a repository somewhere within that samba share. However, only the linux machine is able to access the repository but not other server/client?
This behavior is expected as the mountpoint only exists locally at the linux machine. The Windows Server does not know at all that there is a mountpoint. Even if it did, the Samba server would suddenly have to start asking a client for data within the volume, which doesn’t fit into the Client-Server structure of Samba. So this setup can never work.
To allow others to access the restic mountpoint you’d have to mount the repository into some directory and then use a samba server on the machine to share that directory. That way accesses to the directory are processed by the server which also knows about the mounted repository.