Which is better for a bright living room?

The Samsung S90D. Its QD-OLED panel runs brighter in color and its anti-glare coating cuts reflections better than the Sony's standard OLED finish.

Does the Samsung S90D support Dolby Vision?

No. It handles HDR10, HDR10+ and HLG. The Sony BRAVIA 6 supports Dolby Vision, which matters if you stream Dolby Vision titles.

Which has the better smart TV system?

They suit different habits. Sony's Google TV with Gemini gives hands-free voice search and Google Cast. Samsung's Tizen is fast and works with Alexa and Google Assistant, but its layout is more divisive.

Is the Sony worth stepping up to for gaming?

Only if you want Dolby Vision gaming or DTS audio. Both do 4K/120, VRR and ALLM on four HDMI 2.1 ports, so motion handling is close.

Both use OLED panels with similar lifespans, and neither maker publishes a burn-in rating. The Sony's per-panel factory calibration is the more concrete long-term quality claim.

Can I get the Sony in a larger size?

Yes. The BRAVIA 6 comes in 48, 55, 65, 77 and 83 inches. The S90D listing here is 65 inches only.

Samsung S90D OLED 4K Smart TV vs Sony BRAVIA 6 OLED K77A60

Both are 120 Hz OLED 4K TVs with four HDMI ports, so the picture fundamentals are close. The Samsung S90D uses QD-OLED, which reviewers say gives brighter, more saturated color, and it has a stronger anti-glare coating. The Sony BRAVIA 6 runs Google TV with Gemini voice help, adds Dolby Vision and DTS:X, and comes in more sizes up to 83 inches. Buy the Samsung for a bright room and punchier color; buy the Sony for Google TV, Dolby Vision, and a bigger screen.

Choose the Samsung S90D if you want the brightest, most saturated OLED picture and you watch in a room with daylight or lamps.
Choose the Sony BRAVIA 6 if you want Google TV with Gemini, Dolby Vision and DTS:X support, and a screen size other than 65 inches.

Prices

Sony BRAVIA 6 OLED K77A60: $1,798.00 at B&H Photo-Video-Audio (last seen Nov 12)