Can't mount anything on a rooted android device: not in /proc/mounts

I have a rooted Samsung Galaxy S23 with Android 14 and Magisk 27 installed. I ran

root

successfully and then proceeded to go into

shell

in which I obviously had root rights (#). Then I ran

-o remount,rw /data/adb/service.d

which gave me the error message

: '/service.d' not in /proc/mounts

. This always occurs whenever I try to mount/remount any root directory. How can this be fixed?