firewall for Mac?

Just to add a bit to what @BobTheFisherman has already provided you, macOS already comes with two types of software firewalls. One works at the application layer, the other at the network layer. Both; however, are disabled by default ... as they really aren't needed in most cases on a local network.

The application-layer or socket filter firewall is enabled at System Preferences > Security & Privacy > Firewall; whereas, the network layer one would require that you either use commands in the Terminal app, or use a third-party graphical front-end app to enable it.

Little Snitch would be an example of a third-party application-layer software firewall. The only benefit, that I can see, is that it has more control options vs. the built-in macOS equivalent.

The bottom line? Unless you have specific security issues AND understand firewall rules, you shouldn't need to use them at all.

patricejcgautier wrote:

is an external firewall useful?

Please provide some details and context. Your MacOS includes a firewall. If you are on a local network, your router provides protection. Why are you asking?

There is no need to install third party apps that claim to protect, clean, manage, etc. The MacOS performs these tasks very well. And, if you are on a local network, nothing can access your computer that you do not allow.

patricejcgautier wrote:

thank you. I think I am going to activate the Mac OS Ventura firewall

There is no need to activate your computer's firewall under normal situations. Describe your network environment and why you think you need to activate the firewall.