If you want to use these as (animated versions), you can use tools like the Lively Wallpaper app from the Microsoft Store, which allows you to set high-res video loops or GIFs as your desktop background without significant lag.
For a high-quality Megatron wallpaper, you can find several professional options featuring his various incarnations from the Transformers franchise: Top 4K Megatron Wallpaper Sources 3840x2160 Megatron 4k Ultra HD Wallpaper">
: Gritty, detailed renders from the Netflix series can be found on Wallpaper.cam . If you want to use these as (animated