It's not a problem on docker desktop for mac or windows. It's only an issue on linux, and only for systems that use iptables as a firewall (typically ubuntu/debian & ufw). And even more specifically it really only affects servers that are in a hosting environment with no other firewall or protection in front--Digital Ocean's default droplet config is a prime example, on AWS by default you have a cloud-specific firewall provided by Amazon's networking.
On your system docker is running in a little virtual machine that has its own linux kernel, virtual peripherals, etc. This gives you an extra layer of security (by pure happenstance) such that the VM has to allow traffic in too.
And this is kind of why this issue is so nasty. You as a mac user might never know that this is a problem or potential footgun. You could happily develop entire production services on your mac, then move them to a shared linux host like Digital Ocean and... uh oh, now your services are open and you had no idea it was even possible.
If you're deploying code without knowing how networking works, you're always going to have problems with this like this.
Perhaps my example was a little too simplified as AWS is my day-to-day cloud host but I find it hard to believe opening up ports on your VM and exposing it to the world and then placing the blame on docker is fair.
On your system docker is running in a little virtual machine that has its own linux kernel, virtual peripherals, etc. This gives you an extra layer of security (by pure happenstance) such that the VM has to allow traffic in too.
And this is kind of why this issue is so nasty. You as a mac user might never know that this is a problem or potential footgun. You could happily develop entire production services on your mac, then move them to a shared linux host like Digital Ocean and... uh oh, now your services are open and you had no idea it was even possible.