Ok, so indeed, the deployment version was wrong on the extensions. My bad! I assumed that setting the main target deployment target would cover the extensions as well.

That's a good catch. I am using both and ES and an NE. For both of them I am getting the same error. I believe the deployment target is correct since the same app is working just fine on Sequoia 15.6

It makes sense. The AppIDs do show up in the Identifiers page. Thanks for clarifying everything!

I followed once again your steps and now it seems to work. The only difference I see for now is the Bundle Identifier. Why does it work out of the box only by adding the Team ID in ViewController.m ? Shouldn't it require an existing identifier with all the necessary entitlements in the Apple Development Program account?

I am following pretty much the same steps, but with no luck. Question regarding step 13 : you said that you enabled the extension. Do you mean that you enabled only the extension and not the App Bundle containing the extension? In the meanwhile I dug a bit more into the logs and I could see another error that could help: tccd: [com.apple.TCC:access] Failed to create LSApplicationRecord for file:///Library/SystemExtensions/34CA2880-358B-4E1B-BB5D-FE3AD9022E4D/com.X.Y.systemextension/: 'The operation couldn’t be completed. (OSStatus error -10811.)' It looks kind of similar to this and this. Do you have any idea what's the status for the feedback tickets opened as a follow up of these posts? Do you think they might be related to my case?

It does persist after a restart. I am using the automatic signing in XCode