Is it possible to have the popup maximized right when the user clicks on the feature through hosting the webapp or through webapp builder for developers?
Yes this is possible when using WAB Developer and self hosting your app.
Would you do this through the PopupManager.js?
There is a custom widget for this called the Popup Panel Widget Version 2.17 - 9/1/2020 When added to the Jewlerybox theme you can have the popup in the themes Left pane. See the live preview in the link above.
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