In SharePoint default forms, you can change the permissions of an item and publish it when you want, but the same behavior is not available in SharePoint custom forms customized with Power Apps.
In the SharePoint default form, you can reference the item when you create a new list item. However, in the form customized by Power Apps, if the permission level for list browsing is set to "View application page," "View page," or "Open permission" on the SharePoint list, the following message will be displayed when the list item is newly created: "This app is not opening properly. There may have been a permission problem while opening the app." and I cannot browse for items.
So I added "Show Items" to the "Permission Levels for List Browsing" and now the SharePoint list items are also visible in the custom form.
However, this is not the same behavior as the SharePoint default form.
The difference in functionality between the SharePoint default form and the form customized with Power Apps is confusing to use, so I think it will be easier to use if the behavior is unified.