There are sporadic reports from users that, after restoring a Catalina system from Time Machine backups, a new folder appears on their Macs named AppleInternal. This can appear on both the System and Data volumes, and might seem worrying.
The AppleInternal folder isn’t new with Catalina. It’s a standard in-house device used by many of Apple’s engineers to keep those tools which generally aren’t released to the public. Some versions of Xcode, Apple’s software development environment, may look for this folder, and when they find it they can support otherwise hidden features: be careful if you try using those, as they’re not intended for public release.
Having an AppleInternal folder on your Mac shouldn’t have any adverse effects on it. It’s (almost guaranteed to be) empty and otherwise without purpose.
There’s one slight complication in Catalina, though. This folder is actually located on your Data volume, but there’s a firmlink to it from the System volume, so that it can be accessed either as /AppleInternal or via its ‘real’ path of /System/Volumes/Data/AppleInternal.
Whether you’re running Catalina or an earlier version of macOS, if you want to tidy up and remove this folder, all you have to do is delete it, perhaps authenticating as an admin user when prompted. But in Catalina, you can’t directly remove the firmlink, which is set in the system’s list of firmlinks in /usr/share/firmlinks. As you can’t (and shouldn’t) edit that, because it’s on the read-only System volume, all you have to do is locate the folder on your Data volume, trash that, and restart.
It’s a bit of a pain to locate in the Finder, but you can trace it through Finder’s Location list with your Mac name, then Macintosh HD > System > Volumes > Macintosh HD, which is actually the mount point of the
Macintosh HD - Data volume. Drag that copy of the AppleInternal folder to the Trash, empty, and restart. During the restart process, macOS won’t be able to find the firmlinked folder on your Data volume, and it should also vanish from the root level of /AppleInternal. That’s the magic of the Volume Group and its firmlinks.
That said, I am aware that some users are reporting more serious issues with restoring from Time Machine backups in 10.15.3, and that it sometimes doesn’t prove possible to remove the AppleInternal folder. Hopefully, Apple will get to the bottom of this shortly.
Thanks to James for alerting me, and for discussing this issue.