My Q Camera connection issue

Since the cameras do not support 802.11ac the operations of 802.11ax would also probably cause problems. If you have an extender that supports 802.11 b/g/n and can locate one so it can provide a stronger signal where the camera is in the garage that might be a functional solution. If the TCP and UDP ports are blocked by the T-Mobile gateway that could be a problem as it will not reach their servers. The router should be no further than 50-150 feet from the myQ Smart Garage Camera. You might need to take a client to the garage that is 802.11n and check the signal. Maybe something was moved into the garage that impairs the wireless signal. If you have an Android phone you can download a wireless scanner app and scan for the signal and see the strength in the garage. If the camera LED is flashing blue/green it just tells you it can't connect but not really why it can't. 

According to Chamberlain: (Recommended router settings.)

• Set your network to broadcast and not hidden. myQ cameras may work properly with a hidden network, but this is not recommended.
• Ensure you have DHCP enabled. DHCP allows the router to assign a LAN IP address to the myQ camera.
• >myQ cameras are compatible with both 2.4 GHz and 5 GHz Wi-Fi.
• Ensure you have 802.11n (802.11 b/g/n) enabled. myQ cameras do not support 802.11ac
• Set your router's security to WPA2. While myQ products support other security protocols, WEP and WPA, security protocol WPA2 is recommended. WPA2 Enterprise and WPA3 Enterprise settings are not compatible with myQ product

myQ cameras require these ports in order to communicate to our server

• Inbound and outbound TCP/UDP ports 9122, 4444, 5101-5104, and 4101-4104 open

Verify that ports are not being blocked by your router or a firewall product

• If you have your router's MAC address filtering enabled, the MAC addresses of the myQ product must be added to the list of authorized devices. You can review the MAC addresses of all devices on your network with your router's software.

Since T-Mobile has no provision to allow for unblocking the ports, should they be blocked, there is not much that T-Mobile users can do about that.

If you are not using any newer clients with 802.11x reducing the 2.4 GHz to n/g should not be a problem and should allow the camera to connect via 802.11n on the 2.4 GHz radio.