No longer has the ability to customize a SharePoint list forms using Power Apps

Hi @john john Pter,

Per my test, there is no such button on the new item form and edit form, SharePoint might removed it in recent update

As a workaround, you could custom the form in the command bar, select Integrate -> Power Apps -> Customize forms.

And choose to custom edit form new item form and view form in the default mode

And here is the details for your reference

https://zcusa.951200.xyz/en-us/power-apps/maker/canvas-apps/customize-list-form

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