Great Thanks to @DTS Engineer, @Papaductions . I tested at iOS26 beta 5, but it still happens. So, I hope this is resolved in the iOS 26 GM/official release.

Also, exactly how many blocked numbers can be registered in CallKit’s block number list?

I agree with you. However, while developing the app, I realized that comparing more than ten million numbers every time a call comes in wouldn’t be an easy task either.