I'm trying to develop a Safari app extension and want to enable a persistent background page for it. I could find examples of how to enable it for Web extensions using manifest.json, but for App Extension it seems that I need to use Info.plist and I couldn't find any documentation on it. How can I use the background page?
Safari App Extensions and Safari Web Extensions are two different extension technologies. Safari App Extensions are limited to macOS but Safari Web Extensions are supported on macOS, iOS, iPadOS, and visionOS. Do you want to continue to build a Safari App Extension or do you mean to build a web extension? Persistent background pages are also only available on macOS, but we encourage you to explore using a non-persistent background page or service worker for broader support and better performance.
The documentation for web extensions is available here.