How am I supposed to fix a disk from single user mode?

I have an orphan directory on my main disk. 1. I restart the computer in single user mode. 2. In single user mode, the main disk / is mounted as read-only. 3. I type /sbin/fsck -fy. 4. fsck points the problems but does not fix them. I suppose because the disk must be unmounted or because the disk is read-only. 4. I try to unmount the disk by using umount / or umount /dev/disk2s1, I get a Resource busy, try diskutil umount error. 5. I try diskutil umount. I get an error telling me that diskutil cannot run from single user mode. The main disk is APFS. WTH is that? How am I suppose to fix the problem?