Impossible to customize a product page

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I have recently found it impossible to change the template of the product pages. As you can see from the screen, the pages are in light grey, without the possibility of selecting and editing them. At first I thought it was the GemPages builder, but assistance told me it might be the 'Flow' theme. So I deleted GemPage App and change

Theme. Despite changing the Theme (also switching to 'Dawn') the problem persists.

Help me understand what it could be. Thanks