fsck_apfs not working from terminal in single user mode

I am trying to fix errors on my MacIntosh HD Data volume. I have tried to fix using Disk Utility from normal mode and from recovery mode. Same problem. DI hangs at a certain point and that's it. I boot into single user mode. Using df -h I see that the MacIntosh HD Data volume is /dev/disk2s1. I try to type: fsck_apfs -y /dev/disk2s1 and I get this: > error: device is unreadable because you are in single user mode. I try the same command from normal boot and I get > error: container /dev/rdisk1 is mounted with write access. I have done this thousands of times before, from single user mode. This is some Catalina crap. How do I do that now on Catalina?