Can't edit hosts file on macOS 13.5 (sudo not working)

I don't have permission to edit the hosts file, even if I use sudo and turn off SIP. I use sudo vim /etc/hosts to open the hosts file. After entering :wq!, it shows: "hosts" E212: Can't open file for writing like I am not using sudo. I also tried using sudo nano /etc/hosts and it said: [ Cannot open file for writing: Operation not permitted ] Then I try sudo chflags nouchg /etc/hosts, but it makes no change. BTW, inside the Finder, there is a lock in the lower-left corner of the hosts file. I try to change the lock status in **Get info** but the lock icon is not clickable.