Which is better for gaming?

The Samsung M80H has the higher 144Hz refresh and Mini-LED contrast. The TCL T7 runs 120Hz with four HDMI ports, which is enough for most consoles. Pick the Samsung for competitive play, the TCL for a bigger shared screen.

Which has the better picture?

The Samsung's Mini-LED dimming gives deeper blacks and less blooming in dark scenes. The TCL's QLED panel is brighter and more colorful in a bright room. The Samsung wins on contrast, the TCL on size.

Is the TCL worth it for a large living room?

Yes. At 65 inches it fills a big wall better than the 55-inch Samsung. If your seating is far back, the extra size matters more than Mini-LED dimming.

Both are LED-based and should run for years with normal use. Samsung's build and smart platform updates have a longer track record; TCL's value is strong but its software support is shorter.

Should I step up to the Samsung?

Step up if you want Mini-LED contrast, Bluetooth, Ethernet and the newer Tizen platform in a smaller room. Stay with the TCL if screen size is your priority.

TCL 65" T7 Series QLED TV vs Samsung M80H 4K Mini-LED Smart TV

Buy the TCL T7 if you want the bigger 65-inch screen and a true QLED panel with wide color for the same kind of budget. Buy the Samsung M80H if you sit closer, want Mini-LED backlighting, Bluetooth and Ethernet, and the newer Tizen/One UI smart platform. The TCL gives you more screen per dollar; the Samsung gives you better contrast control and a more complete smart TV.

Choose the TCL T7 if you want a 65-inch QLED with 120Hz gaming and four HDMI ports for a mixed movie and console setup.
Choose the Samsung M80H if you want Mini-LED contrast, Bluetooth and Ethernet in a 55-inch size for a smaller room.

Prices

TCL 65" T7 Series QLED TV: $529.99 at Amazon (checked today)
Samsung M80H 4K Mini-LED Smart TV: $397.99 at PC Richard & Son (checked today)
Difference: the Samsung M80H 4K Mini-LED Smart TV is $132.00 cheaper than the TCL 65" T7 Series QLED TV today