Hello Airborne-Macintosh,
Welcome to Apple Support Communities.
We understand that you’re not able to share files when the firewall is enabled. We are happy to help.
Have you ever been able to share files with the firewall enabled? When you factory reset your Mac, did you test without reinstalling your backup? If so, what were the results?
Please try the steps here: Block connections to your Mac with a firewall - Apple Support
"Set firewall access for services and apps
- On your Mac, choose Apple menu
> System Settings, click Network 
in the sidebar, then click Firewall. (You may need to scroll down.) - Click Options.
- If the Options button is disabled, first turn on Firewall.
- Click the Add button
under the list of services, then select the services or apps you want to add. After an app is added, click its up and down arrows 
and choose whether to allow or block connections through the firewall. - Blocking an app’s access through the firewall could interfere with or affect the performance of the app or other software that may depend on it.
- Important: Certain apps that don’t appear in the list may have access through the firewall. These can include system apps, services, and processes, as well as digitally signed apps that are opened automatically by other apps. To block access for these programs, add them to the list.
- When your Mac detects an attempt to connect to an app you haven’t added to the list and given access to, an alert message appears asking if you want to allow or deny the connection over the network or internet. Until you take action, the message remains, and any attempts to connect to the app are denied."
If no issue resolution, we recommend doing some isolating troubleshooting steps to test in safe mode and new user account.
How to test in safe mode: How to use safe mode on your Mac - Apple Support
"Apple silicon
- Shut down your Mac.
- Turn on your Mac and continue to press and hold the power button until you see the startup options window.
- Select your startup disk, then press and hold the Shift key while clicking “Continue in Safe Mode.”
- Log in to your Mac. You might be asked to log in again.
Intel processor
- Turn on or restart your Mac, then immediately press and hold the Shift key as your Mac starts up.
- Release the key when you see the login window, then log in to your Mac.
- You might be asked to log in again. On either the first or second login window, you should see ”Safe Boot” in the upper-right corner of the window."
How to create a new user account to test: Change Users & Groups settings on Mac - Apple Support
"Create a new user or group.
Click the New Account pop-up menu (you may be asked to enter your password), then choose a type of account.
- Administrator: An administrator can add and manage other users, install apps, and change settings. The new user you create when you first set up your Mac is an administrator. Your Mac can have multiple administrators. You can create new ones, and convert standard users to administrators. Don’t set up automatic login for an administrator. If you do, someone could simply restart your Mac and gain access with administrator privileges. To keep your Mac secure, don’t share administrator names and passwords.
- Standard: Standard users are set up by an administrator. Standard users can install apps and change their own settings, but can’t add other users or change other users’ settings.
- Sharing Only: Sharing-only users can access shared files remotely, but can’t log in to the computer or change settings. To give the user permission to access your shared files or screen, you may need to change options in File Sharing, Screen Sharing, or Remote Management settings. See Set up file sharing and Share the screen of another Mac.
- Group: Groups allow multiple users to have the same access privileges. You control a group’s access to your shared folders by setting access permissions in the File Sharing options in Sharing settings.
See Add a user or group."
Let us know if you have further questions.
Take care.
