I'm trying to fix an external drive by entering

sudo fsck_hfs -fy /dev/disk4s2

in the terminal and the result is

** /dev/rdisk4s2 (NO WRITE)
Can't open /dev/rdisk4s2: Resource busy

I've already tried

diskutil unmountDisk force /dev/disk4s2

and it won't help.

Full disk access is granted to the terminal in security system preferences.

I'm running macOS Ventura on an M1 Max.

Any ideas on how to fix this?