I've been trying to submit my photos but all of them got rejected for some reason

The screenshot above demonstrates the use of Photoshop’s Photo Warming Filter applied to an Adjustment Layer. Before on the left. After on the right. 

Ideally, white balance should begin at the camera with a proper light or AWB setting.

https://www.adobe.com/creativecloud/photography/technique/white-balance.html  

Hope that helps.

the duck with the grass
It’s been mentioned it’s too centred: consider moving it to the left. Have space for copy/ content to be written. It is a great image for leading our eye to the right side of the screen. We want to look where the duck is looking.

PS has the generative expand option: 9:16 w plenty of space on the right side.
Remove the grass on the duck, around the duck and in the reflections. 
Duck in water. 650 000+ images on Adobe Stock (similar content rejection may also occur)

Cheers

nate

I assume they were rejected for Quality/Technical issues as described in your Contributor User Guide. 

https://helpx.adobe.com/stock/contributor/help/quality-and-technical-issues.html

Other Reasons for Rejection:

https://helpx.adobe.com/stock/contributor/help/reasons-for-content-rejection.html

Stock has a generous inventory of ducks. This is what you’re competing with:

https://stock.adobe.com/search?k=wild+ducks

https://stock.adobe.com/search?k=wildlife+ducks

Hope that helps.

too dark, poorly cropped and the white balance by the duck is too cold.

It should look something like this:
 

The bird is too small.
You should have used a longer telephoto lens.
Also, since it's centered in the frame, it would be better if you paid more attention to the composition.

The photo below has a blue white balance.