log in failed both in SSMS and Windows over VPN to remote Server

I would appreciate your guidance on this matter. There are several issues occurring simultaneously, and I am weak in networking.

I have created a PPTP VPN to connect to the server via Global IP and the internet. This has been done through Routing and Remote Access on Windows Server 2019. Additionally, a user named UserVPN, which is part of the Administrator group, has also been defined on the server. The VPN connection connects to this user. My local IP on the network is 192.168.1.4, and the local IP of the server on the remote network is 192.168.1.92. When the VPN connects to the remote server, a second IP is added, which is displayed as 192.168.2.11 on the client computer using the CMD command ipconfig /all.

The issues that have arisen are as follows:

When entering //192.168.2.11/ in the RUN window, I am prompted for the username UserVPN, but it does not accept the password, and I cannot access the shared folders. It does not accept the Administrator username and its password either. I am sure that I have entered the passwords for both users correctly.
I also entered this IP for SSMS, but it does not accept the sa password and displays the message “Login failed for user ‘sa’.”
I should mention that network discovery is enabled on the Windows Server, and the firewall is turned off.