[Android Software/Hacking General [Developers Only]] osm0sis:
There shouldn't be anything left mounted... 🤔

busybox-ndk/customize.sh at master · Magisk-Modules-Repo/busybox-ndk

busybox-ndk. Contribute to Magisk-Modules-Repo/busybox-ndk development by creating an account on GitHub.

github.com

And for a -system install it should have the real system mounted at /system_root and /system:

busybox-ndk/customize.sh at master · Magisk-Modules-Repo/busybox-ndk

busybox-ndk. Contribute to Magisk-Modules-Repo/busybox-ndk development by creating an account on GitHub.

github.com

Edit: Some pretty wild mount-related errors in the log, however! Reminds me of when /system would get mounted before apex. I'll see if I can reproduce on one of my devices. (y)

Installing zip file '/sdcard/Download/UPDATE-Busybox.Installer.v1.34.1-ALL-signed.zip'
I:Update binary zip
Verifying package compatibility...
Package doesn't contain compatibility.zip entry
I:Extracting updater binary 'META-INF/com/google/android/update-binary'
I:Zip does not contain SELinux file_contexts file in its root.
Archive: /sdcard/Download/UPDATE-Busybox.Installer.v1.34.1-ALL-signed.zip
inflating: customize.sh
Archive: /sdcard/Download/UPDATE-Busybox.Installer.v1.34.1-ALL-signed.zip
inflating: diffusion_config.sh
inflating: module.prop

Busybox Installer Script
by osm0sis @ xda-developers

Mounting...
losetup: /dev/block/loop0=/dev/urandom: Invalid argument
mount: losetup failed 1
/tmp/updater: /dev/tmp/customize.sh[538]: /system/bin/mount: No such file or directory
/tmp/updater: /dev/tmp/customize.sh[538]: /system/bin/grep: No such file or directory
/tmp/updater: /dev/tmp/customize.sh[538]: /system/bin/rm: No such file or directory
/tmp/updater: /dev/tmp/customize.sh[538]: /system/bin/mkdir: No such file or directory
/tmp/updater: /dev/tmp/customize.sh[538]: /system/bin/mount: No such file or directory
/tmp/updater: /dev/tmp/customize.sh[541]: /system/bin/basename: No such file or directory

Extracting files...
/tmp/updater: /dev/tmp/customize.sh[546]: /system/bin/mkdir: No such file or directory
/tmp/updater: /dev/tmp/customize.sh[547]: cd: /dev/tmp/busybox-ndk: No such file or directory
/tmp/updater: /dev/tmp/customize.sh[548]: /system/bin/unzip: No such file or directory
/tmp/updater: /dev/tmp/customize.sh[549]: /system/bin/chown: No such file or directory
/tmp/updater: /dev/tmp/customize.sh[549]: /system/bin/chown: No such file or directory
/tmp/updater: /dev/tmp/customize.sh[549]: /system/bin/find: No such file or directory
/tmp/updater: /dev/tmp/customize.sh[549]: /system/bin/find: No such file or directory

Installing...
/tmp/updater: /dev/tmp/customize.sh[586]: /system/bin/grep: No such file or directory
/tmp/updater: /dev/tmp/customize.sh[586]: /system/bin/tail: No such file or directory
/tmp/updater: /dev/tmp/customize.sh[586]: /system/bin/cut: No such file or directory
/tmp/updater: /dev/tmp/customize.sh[586]: /system/bin/grep: No such file or directory
/tmp/updater: /dev/tmp/customize.sh[586]: /system/bin/tail: No such file or directory
/tmp/updater: /dev/tmp/customize.sh[586]: /system/bin/cut: No such file or directory
Unknown architecture:

Your system has not been changed.

Script will now exit...

/tmp/updater: /dev/tmp/customize.sh[586]: /system/bin/awk: No such file or directory
/tmp/updater: /dev/tmp/customize.sh[586]: /system/bin/find: No such file or directory
/tmp/updater: /dev/tmp/customize.sh[586]: /system/bin/umount: No such file or directory
/tmp/updater: /dev/tmp/customize.sh[586]: /system/bin/rm: No such file or directory
Updater process ended with ERROR: 1
I:Install took 5 second(s).
Error installing zip file '/sdcard/Download/UPDATE-Busybox.Installer.v1.34.1-ALL-signed.zip'

@AnonVendetta Can you verify that your device is system-as-root, and then show me the contents of /system_root/system/apex (alternately /mnt/system/system/apex) when the system partition is mounted in recovery?