Did you refer to New item form in the SharePoint list?
Per my test, the New item form is a three-column layout.
Currently, there is no Microsoft plan to improve this experience by opening the popup full screen.
Meanwhile, to get this option in the SharePoint list, I recommend you give suggestion in the feedback portal and help to make improvements. Many features of current products are designed and upgraded based on customers’ feedback. With requirements like this increase, the problem may well be released in the future. Thanks for your understanding and support.
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