Do you still want to move away useless built-in apps on OS X 10.15? It has changed the OS layout on the filesystem so that the built-in applications are in /System/Applications/ instead of /Applications/ now. That area is also more protected, so we’ll need to add an extra step to move away that crap.
Initial move
Even though all applications are still shown to be in /Applications/ in Finder, the system ones are actually in /System/Applications/:
It’s interesting that remounting / back as read-only doesn’t work; you need to reboot to do that.
123
$ sudo mount -ur /
mount_apfs: volume could not be mounted: Invalid argument
mount: / failed with 66
If you don’t want to do any other system modification at this time, it’s a good idea to reenable SIP.
Note: If you’re upgrading from OSX 10.14, you may want to move /Applications/junk/ to /System/Applications/junk/ to be consistent instead of creating a new directory as described above.
Upgrades
It’s very likely that you’ll need to move pieces of those apps to junk/ after a system upgrade. Here’s an example upgrade from 10.15 build 19G73 to 19H15.
We can find the apps that need to be moved again (this is just an informative step, you don’t have to do it):