The Power Apps screen has a text label control, an image control, and a button control. My requirement is that when user adds text in text input, it will be added inside the image control, and if the user clicks on the download button, then the image will download in PNG format along with the text.
Still, I am not getting any clue to achieve this requirement, could you please give any suggestion?

In Powerapps, when you think to donwload an image/pdf/etc (irrespective of type), then you should assume that it has been uploaded to a space/SharePoint etc And you should have that URL in power app's UI.
Then on the button click using the below method to download