Previously I miss changed the sudoers file, and unfortunately sudoers file be locked. After that, I tried to copy sudoers and save it to original path. It start throw 502 error to me:

sudo: /etc/sudoers is owned by uid 502, should be 0
sudo: no valid sudoers sources found, quitting
sudo: unable to initialize policy plugin

This is because after I copy sudoers and replace old file, the new file missing the system read authority. The correct file permissions should be:

Final Solution

https://apple.stackexchange.com/a/353478

Try Flow

Basically, I tried this page solutions: https://apple.stackexchange.com/questions/157772/sudo-etc-sudoers-is-owned-by-uid-501-should-be-0

The first I tried is: https://apple.stackexchange.com/a/157775, go into single user mode by cmd+S, and following this command:

mount -uw /
chown root /etc/sudoers
chmod 440 /etc/sudoers
reboot

However, I stuck at mount -uw /, it shows me error like:

Updating mount from `disk` to read/write mode is not allowed.
mount_apfs: volume could not be mounted: Operation not permitted
mount: / failed with 77

After searching, refering this link: https://apple.stackexchange.com/a/401963I, I got that this happen because in MacOS Catalina, System Integrity Protection(SIP) is active. We have to go into Recovery Mode to run the command.

OK.

• Hold cmd+R, go into recovery mode
• Disk Utilities > Select Macintosh HD, and Mount confirm disk is under Mount
• Close Disk Utilities
• NavigationBar: Utilities > Terminal
• Type: chown root:wheel "/Volumes/Macintosh HD/etc/sudoers"
• reboot

🎉 After computer restarted, tap sudo su to double check, and the error is disappeared now!!

Reference

• https://apple.stackexchange.com/questions/157772/sudo-etc-sudoers-is-owned-by-uid-501-should-be-0
• https://apple.stackexchange.com/questions/401921/sbin-mount-uw-not-working