How can I disable the MAC address filtering or add an acceptable MAC address for my HP 8600 printer?

My suggestion would be to forget MAC filtering.

Your problem is pretty common among T-Mobile Internet users. The following usually fixes the problem.

Add a new WiFi network for the HP. Use the T-Mobile app and tap the Network tab on the bottom, then the "+" button on the lower right. Create a new 2.4 GHz WiFi network with a unique name (SSID), just for your printer. Make sure the WPA type is WPA/WPA2. This is different from your main network which, by default, is WPA2/WPA3.

Now, go to your printer and clear out all of the information you have entered for your printer's setup and then connect your printer to your new wireless connection. See if that doesn't help.

¡Buena suerte!