Is the Firewall for Catalina 10.15.7 effective enough to prevent LAN users from accessing my Mac?

The Firewall per se is not going to prevent users from accessing your Mac.

If others on your LAN can connect with your Mac then you probably have File Sharing and/or other sharing or remote management services turned on.

On your Catalina Mac, do the following:

• Go to System Preferences > Sharing and make sure all services listed are turned OFF (UNchecked).

• Go to System Preferences > Security & Privacy > Firewall > Advanced and turn ON (CHECK) "Block all incoming connections."

• Go to System Preferences > Security & Privacy > General > Advanced, turn on (CHECK) "Require an administrator password to access system-wide preferences."

When you exit System Preferences make sure the lock icon in the lower left corner of the System Prefs window is locked. If it shows unlocked, click the lock to prevent further changes.

And then you should also make sure no one can manually log onto your Mac to turn any of these settings back on. You may need to change the passwords for any/all user accounts on your Catalina Mac. Especially for all admin accounts. And then keep them secret.

Yes, the firewall is supported. There are also tools you can use to control the packet-filtering level firewall (the built-in in System Preferences is an application-level firewall, although its setting for blocking all incoming connections is pretty good).

However, if you have sharing services turned on, or if there is remote desktop software on your computer that these people are using, then those will deliberately open holes in the firewall.

[Edited by Moderator]

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