For Mac OS Lion to Big Sur and all version featuring the Apple Mac App Store, (including Mojave, Catalina) , you would need to download the free windows remote desktop connection client provided by Microsoft. 

The application would allow you to connect to your Windows VPS. 

You may find the app to download from the link below : 

https://apps.apple.com/us/app/microsoft-remote-desktop/id1295203466?mt=12

The remote desktop client supports several RDP connections. Therefore, you may reiterate these steps if you own several Windows VPS. You'll be then be able to connect to any of these simultaneously or individually.

Here is how to configure your Remote Desktop in the RDP App. 

1) Install the Application on your computer

2) Once, the application is installed, you would need to open the app and click on the "+" and then click "Add PC"

3) In the prompt opened, you are asked to type in the "PC Name" field a hostname or IP address. Type the IP address of your Windows VPS that you configured inside SolidCP during the VPS creation. NOTE: The hostname provided with your VPS doesn't resolve to your IP and wouldn't work. In the Friendly name field, you may use any name you see fit. 

4)  In the User Account Dropdown click on "Add an User Account"

5) In the opened popup set your Username with "Administrator". Or if you define another user session inside your Windows VPS you may use this username but the default would remain Administrator. And type the password you have configured during the initial Windows VPS installation and click "Add"

6) You may leave the others settings to default and click on Add on the Main Prompt. 

That's it! You have configured your Windows VPS within your Mac OS Remote Desktop app and you'll be able to access it at any time by double clicking its icon on the main app view. 

Then, you would need to enter the information you received in the email named "New Windows VPS information". 

That's it! You should be connected to your Windows VPS. 

If you need further assistance, you can open a support ticket from your client area.