The latest version of tcl-tk that gets installed with the home-brew brew command on MacOS is 8.6.15.
It looks like the toolchains are expecting 8.6.11_1, because they have a Cellar/tcl-tk/8.6.11_1 directory but no 8.6.15 directory.
So I had to
$ ln -s /opt/nordic/ncs/toolchains/<toolchain of interest or any relatively new toolchain>/Cellar/tcl-tk/8.6.11_1 /usr/local/Cellar/tcl-tk/8.6.11_1
to make guiconfig work.
Can you deliver the toolchain so that more recent tcl-tk packages from homebrew work? Thank you.
Regards,
Burt Silverman