Mount /system on Android 10 with Magisk I am using Magisk 20.4 and trying to mount /system on a Google Pixel (1st gen) running Android 10.
I have tried using:
adb shell su -c mount -o rw,remount /system

that gives:

mount: '/system' not in /proc/mounts

The following also do not work:
adb shell su -c mount -o rw,remount /


'/dev/root' is read-only

adb shell su -c mount -o rw,remount /sbin/.magisk/mirror/system_root


'/sbin/.magisk/block/system_root' is read-only

I was also curious whether stuff in /sbin/.magisk/rootdir/system/ can actually override stuff in /system/ but that doesn't seem to be the case..
Has anyone managed to mount /system on Android 10? Is this issue specific to Google Pixel?
Cheers,
Paschalis
EDIT:
trying Hack5 suggestion, it gives me:

mount: '/system' not in /proc/mounts

Since I knew that /sbin/.magisk/mirror/system_root was a valid mount point, Ive tried the following, which still fails:
mount -wo remount /dev/block/bootdevice/by-name/system$(getprop
 ro.boot.slot_suffix)  /sbin/.magisk/block/system_root


mount: '/sbin/.magisk/block/system_root' not in /proc/mounts

EDIT2:
Turns out it's impossible to mount /system on a factory image of Google Pixel. But, I was missing the whole point of Magisk! So I made a few modules and I can override/add the system libs and bins that I need. There is even support for apex on Android 10!
Your second command is correct, but the virtual block device is read only. IIRC, this is caused by the a/b mapping virtualisations.

Referring to https://android.stackexchange.com/a/158890/171244, you can see that specifying the correct block device will help. Try:

adb shell
su -c mount -wo remount /dev/block/bootdevice/by-name/system$(getprop ro.boot.slot_suffix) /system


This will switch from the virtual mapper (/dev/root) which is read-only, to the actual partition block device, making it writable