Today, Google announced the arrival of a long-awaited feature on its Gmail app for iPadOS. It finally supports Split View, meaning that you can use it side-by-side with other apps.
This means that you can drag and drop images into an email from apps like Google Photos and the native Photos app. Another use case would be to have another app open to use as a reference when composing an email, or to have an app open to take notes from an email that you're reading.
This is also going to come in handy with iPadOS 14, which is going to be available later this year. The feature update will actually let you run two instances of the same app in Split View, so you'll be able to do things like drag and drop content from one email to another.
The app update is available now. As long as you have automatic updates turned on, it should arrive shortly. If not, you can always update the app manually here.