Many thanks again for your advice.

I ran the two commands you recommended:

root@fart:/home/mikef/gentoo#  chmod 4755
/home/mikef/gentoo/usr/lib64/chromium-browser/chrome-sandbox
root@fart:/home/mikef/gentoo# chown root
/home/mikef/gentoo/usr/lib64/chromium-browser/chrome-sandbox
root@fart:/home/mikef/gentoo# /home/mikef/gentoo/usr/bin/chromium
[2098:2098:0628/083242.274727:ERROR:zygote_host_impl_linux.cc(89)] Running
as root without --no-sandbox is not supported. See https://crbug.com/638180.
root@fart:/home/mikef/gentoo#

I also tried running chromium as a user:

mikef@fart:~$ /home/mikef/gentoo/usr/bin/chromium
[2105:2105:0628/083309.657067:FATAL:setuid_sandbox_host.cc(157)] The SUID
sandbox helper binary was found, but is not configured correctly. Rather
than run without sandboxing I'm aborting now. You need to make sure that
/home/mikef/gentoo/usr/lib64/chromium-browser/chrome-sandbox is owned by
root and has mode 4755.

Maybe I need to talk to the chrome community.....

Regards

MF