google-chrome Failed to move to new namespace

Although this doesn't answer your question, since it you can't set security-opt, this is still a good solution for other people with a similar problem finding the question.

Download this chrome.json file, which contains a custom security profile.

Use the security profile with --security-opt seccomp=path/to/chrome.json or with docker-compose:

# docker-compose.yml
version: '3'
services:
  <service name>:
    #
    # the service configuration
    #
    security_opt:
      - seccomp=<path to downloaded chrome.json>

see https://stackoverflow.com/a/53975412/8678740

After researching extensively internet I think I found the answer:

Sandboxing  For security reasons, Google Chrome is unable to provide sandboxing when it is running in the container-based environment. To use Chrome in the container-based environment, pass the --no-sandbox flag to the chrome executable

So it looks like there is no better solution than --no-sandbox for me, even though its not being very secure, there are people on the internet claiming that it is still safe to use "--no-sandbox" as its running within container which is extra protected any way.