Projects tab disappears after uninstalling Divi

I recommend getting in touch with Divi’s support about this via https://divi.help or https://www.elegantthemes.com/contact/ – as this is a commercial plugin/theme they cannot help you here with it.

When you uninstall the DIVI theme, your projects disappear because they rely on DIVI-specific modules, shortcodes, or custom settings. These elements don’t transfer to other themes. Reinstalling DIVI restores the projects as the theme’s structure and content are reintegrated. To avoid this, consider converting custom layouts to a more universal format before switching themes.