As the USB 2.0 link used with Lightning does not have the bandwidth for 1080p HDMI, compression was used, requiring a pretty beefy processor in the adapter. Some enterprising people at the time ...

Plugable USBC-7400H4 adapter supports four HDMI outputs and 90W power delivery Multi-display support for Windows, macOS, and Apple M4 laptops Quad 4K at 60Hz plus virtual 8K monitor via USB-C Plugable ...

Use a USB-C to HDMI adapter or the Steam Deck Dock Connect ... so you’ll see the best results when connecting to a 1080p TV or monitor.