root access - Why (bind) mounts in /storage/emulated/0 are not visible in apps?

I mounted a directory into another directory with:

mount --bind "/storage/sdcard/dir1" "/storage/sdcard/dir2"

I do this at boot completion with Tasker. I can see the mounted files in adb shell and in Termux, even as non-root user. But I can not see these files in apps like Total Commander or my Music Player.

I use Lineage 7.1.2.

In this thread, a solution is to switch off "mount namespaces" in SuperSU. Unfortunately, I have the LineageOS default SU app which does not seem to provide such option. Any suggestions?