Can I view or change my background for my Windows instance on Lightsail?

The limitation you're experiencing is related to using the browser-based RDP client in the Lightsail console. When you connect through the "Connect using RDP" feature in your web browser, certain visual features like custom backgrounds are typically disabled to optimize performance and bandwidth usage during the remote desktop session.

To view and change your Windows instance background, you can connect using a full Remote Desktop client instead of the browser-based option. You have two alternatives:

1. On Windows: Use the Remote Desktop Connection (RDC) client that comes included with the Windows operating system. You'll need your instance's public IP address and the administrator username and password to connect.

2. On macOS: Install the Microsoft Remote Desktop application from the App Store. Once installed, add your instance using its public IP address, then connect with the administrator credentials.

When you connect using these full RDP clients rather than the browser-based client, you should have access to all Windows personalization features, including the ability to view and change your desktop background. The full clients provide a more complete remote desktop experience with fewer restrictions on visual elements.
Sources
Connect to a Lightsail Windows instance from macOS with Remote Desktop - Amazon Lightsail
Connect to your Lightsail Windows instance using RDP - Amazon Lightsail
Connect to a Lightsail Windows instance from Windows with Remote Desktop - Amazon Lightsail