when will magic keyboard for ipad pro 3rd gen 11inch be release?

I’m not aware of an iPad Pro 11” third-generation model, and the current Magic Keyboard is compatible with the available first and second generation models.

Identify your iPad model - Apple Support

https://www.apple.com/shop/product/MXQT2LL/A/magic-keyboard-for-ipad-pro-11%E2%80%91inch-2nd-generation-us-english

If you’re asking when (if?) Apple might release a new product, nobody here that knows that will discuss that, and the rest of us, well, the rest of us don’t know that.