Which is better for gaming?

The Sony. It has a 120Hz panel, VRR and HDMI 2.1 with low input lag. The Panasonic listing gives no refresh rate or gaming features.

Which has the bigger screen?

The Sony at 77 inches against the Panasonic at 65 inches. That is a full size class apart, so check your room before deciding.

Do both have OLED contrast?

Yes. Both use OLED panels with self-lit pixels, so both give deep blacks and wide viewing angles. The Sony adds its Cognitive Processor XR on top.

Is the Sony worth stepping up to?

If you game, watch in a large room, or want Google TV and screen-based audio, yes. If 65 inches fits your space and you just want an OLED, the Panasonic covers the basics.

Which has better sound out of the box?

The Sony, which uses Acoustic Surface Audio+ to vibrate sound from the panel itself. The Panasonic listing does not describe its audio.

How many devices can I connect?

The Sony lists four HDMI ports plus Ethernet and Wi-Fi. The Panasonic lists HDMI and Wi-Fi but not a port count.

Panasonic 65-inch OLED TV vs Sony Bravia 8 II 77-inch OLED TV

The Sony K-77XR80 is the bigger, more feature-complete set: 77 inches, a 120Hz panel with VRR and HDMI 2.1, Google TV, and Acoustic Surface Audio+. The Panasonic 65-inch OLED is the smaller, simpler option, and its listing gives little beyond 4K OLED, HDR, Wi-Fi and HDMI. For a large living room or gaming, the Sony is the stronger buy. For a smaller room where 65 inches fits and you want a plain OLED, the Panasonic does the core job.

Choose the Panasonic 65-inch OLED if your wall or stand suits a 65-inch screen and you want a straightforward 4K OLED without paying for gaming extras.
Choose the Sony K-77XR80 if you want a 77-inch picture, 120Hz gaming with VRR, and a smart platform with voice assistants built in.

Prices

Panasonic 65-inch OLED TV: $2,299.99 at Amazon (last seen Nov 10)