Qwen Image 2.1 has native 2K (2048*2048) support for direct output.
Output size comes from ResolutionSelector (width/height). Default is 1 megapixel (10241024). For native 2K, set 1:1 and 4 megapixels (20482048). Prefer multiples of 32.
To generate a transparent image, wrap the prompt like this and replace the middle with the subject:
This is an RGBA format image with transparency. [your description]. The image has an alpha channel and a transparent background.
Save as PNG to keep the alpha channel.

Woman in Neon Spotlight
High-Speed Train Through a Mountain Valley
Thousand-Le-Green Style Modern Megacity
Watercolor Lemonade Stand
Restyle a Portrait as a Retro 1980s Photo
Cute Cartoon Dragon Transparent Sticker
Guochao Lion Mask Illustration
Paper-Cut Deer and Moon
Whale Swimming Through a Cloud
Steampunk Airship Deck
Folded Dream City Panorama
Transparent RGBA Cartoon Sticker