[pxc]

Yeah, this is probably because macOS has done something very, very weird, and added an executable `/usr/bin/command` to the system. These are the contents on the old MacBook I have for work right here:

    #!/bin/sh
    # $FreeBSD: src/usr.bin/alias/generic.sh,v 1.2 2005/10/24 22:32:19 cperciva Exp $
    # This file is in the public domain.
    builtin `echo %{0##*/} | tr \[:upper:] \[:lower]` ${1+"$@"}

If you have SIP disabled, try renaming `/usr/bin/command` to `/usr/bin/command.wtf` and see if `tcsh` still acts like there's a `command` command.

[eddieh]

I do have SIP disabled for DYLD_LIBRARY_PATH and a handful of other things, but macOS still says /usr/bin/command is on a read-only file system.

[edit]

Not hard to remount root as writable

    $ sudo mount -uw /
    Password:
    $ sudo mv /usr/bin/command /usr/bin/command.save
    $ tcsh
    % command -v command
    command: Command not found.
    % command -V command
    command: Command not found.
    % 

Now reversing the changes

   % exit
   exit
   $ sudo mv /usr/bin/command.save /usr/bin/command
   $ sudo mount -ur /
   mount_apfs: volume could not be mounted: Invalid argument
   mount: / failed with 66

Looks like I'll have to reboot to get the read-only state back.