Is the TCL QM851G good for bright rooms?

Yes. Its QD-Mini LED backlight reaches very high brightness, so it holds up in sunny rooms and makes HDR highlights stand out. That is its main edge over cheaper LED sets.

Does it support Dolby Vision and HDR10+?

It supports Dolby Vision, HDR10+, HDR10 and HLG, so it handles the main HDR formats from streaming services and discs.

Is it good for gaming?

Yes. It has a high refresh rate panel and gaming features for consoles and PCs, with low input lag in game mode. Check that your console or PC supports the higher refresh rates to get the most from it.

Do I need a soundbar?

Probably, for movies. The built-in speakers handle dialogue but are thin on bass, and Dolby Atmos processing cannot replace a dedicated soundbar or surround system.

How does it compare with the QM8 and QM7?

The QM851G sits at the top of TCL's QM8 line with more dimming zones and higher brightness than the QM7, and better contrast than older QM8 models. It is the pick for a bright room; the QM7 is the step down for darker rooms.