Trouble connecting to older Mac over Wi-Fi

Did you turn off the firewall on each Mac?

can each Mac get on the internet independently, without re-cabling? if so you have a highway (through the Switch portion of your Router) they could share, provided they have something to say to each other.

Did you enter the credentials in the box on the NEW Mac that would allow you to log in and read the correct User files on The OLD Mac? Remember, a User with the same name is NOT the same User on a different Mac -- all Logins and Permissions are Local.

I use File Sharing all the time, and reach MUCH farther back than just Monterey. It works great for me.

I have no idea why yours is not working spectacularly well.

The error message you are getting is what you would get from a Bad Alias file. Are you using aliases to access file on the old Mac?

It may be possible that the router has barred or blocked your device's MAC address on your router has. The MAC address is a unique identifier assigned to each network interface card (NIC) in a device. By blocking a specific MAC address on the router, you can prevent that device from connecting to your Wi-Fi network.

The process of blocking/unblocking a MAC address varies depending on the router's manufacturer and model. Here are general steps to block a MAC address on most routers:

1. Open a web browser on a device connected to the router's network and enter the router's IP address in the address bar. You can usually find the router's IP address on the bottom of the router or in the router's manual.
2. Enter the router's username and password when prompted. If you haven't changed them, the default credentials are often found on the router or in the router's manual.
3. The location of these settings may vary depending on the router's interface. Look for a section related to "MAC filtering," "Access Control," "Wireless Security," or similar.
4. In the MAC filtering or access control settings, there should be an option to add a MAC address to the blocked list or delete a Mac Address from the blocked list. Enter the MAC address of the device you want to block/unblock and save the changes.
5. Apply the changes and restart the router: Once you have removed/added the MAC address to the blocked list, save the settings and apply the changes. Some routers may require a restart for the changes to take effect.

After blocking the MAC address on the router, the device with the blocked MAC address will no longer be able to connect to the Wi-Fi network. Keep in mind that MAC address blocking is not foolproof, as MAC addresses can be spoofed or changed on some devices. For enhanced security, it's recommended to use additional authentication methods such as strong Wi-Fi passwords and encryption protocols.

Possible Fixes:

1. Disable Private Wi-Fi Address:
   1. Go to Settings > Wi-Fi, tap on your work network, and turn off Private Wi-Fi Address.
   2. The router may have whitelisted a specific MAC address; make sure the phone is using the correct one.
2. Turn Off Wi-Fi Assist:
   1. Go to Settings > Cellular > Wi-Fi Assist and toggle it off.
   2. Sometimes, this setting can interfere with connecting to hidden networks.
3. Ensure iPhone Saves the Network Properly:
   1. After manually entering the SSID and password, make sure Auto-Join is enabled.
   2. If the issue persists, try Reset Network Settings (Settings > General > Transfer or Reset iPhone > Reset > Reset Network Settings).
4. Ask IT to Consider Broadcasting the SSID: Hidden SSIDs do not add security and often cause connection instability.

if you have chosen iCloud "Optimize storage":

Optimize storage space

Your Mac can optimize storage by using iCloud to automatically make more storage space available when needed.* It includes built-in utilities to help you quickly find files that are taking up space, and delete any that you longer need.

• macOS Ventura or later: Learn how to optimize storage space

• Earlier versions of macOS: Learn how to optimize storage space

The way I think about that is the Master copy is stored on iCloud. When you need a file, "wait a moment and iCloud will download it for you".

On the newer Mac turn off the firewall.

Just wondering, do you have iCloud Drive enabled?

It messes with Desktop & Documents folders at the very least. they normally do not any longer wzist on your computer. only in Apple's servers on the cloud.