Apple added Split View multitasking to iOS (iPadOS) on the iPad in 2015, with iOS 9, and has continued to improve the feature since. Google has finally added support for Split View in the Gmail app, with the latest update available now.
The omission of the feature has been a complaint from users for years. The advancement, introduced with version 6.0.200531, will let you view multiple Gmail app windows side-by-side. You’ll need the feature enabled within iPadOS: go to Settings > Home Screen & Dock > Multitasking and enable ‘Multiple Apps’.
You can download Gmail for the iPhone and iPad for free from the App Store.