[harryjo]

That doesn't solve the problem that parent incorrectly explained.

    echo "$(false)"

swallows the exit code from $(false).

    $ cat /tmp/test.sh
    set -euvx
    export SHELLOPTS
    echo "$(false)"
    echo "echo of string with failed subcommand does not kill script"
    $(false)
    echo "but consuming exit code does"
        
    $ /tmp/test.sh        
    export SHELLOPTS
    + export SHELLOPTS
    echo "$(false)"
    false
    ++ false
    + echo ''
        
    echo "echo of string with failed subcommand does not kill script"
    + echo 'echo of string with failed subcommand does not kill script'
    echo of string with failed subcommand does not kill script
    $(false)
    false
    ++ false