Which is better for gaming?

The C6. It has four HDMI 2.1 ports, VRR up to 165Hz, G-Sync and FreeSync Premium, and under 0.1ms response. The older set lists 120Hz but no VRR or HDMI 2.1.

Is the C6 worth stepping up to over the older OLED?

Yes for most buyers. You get a brighter evo panel, Dolby Vision, Atmos, current apps and full gaming support. Step down only if you want a curved screen or 3D.

Both use OLED panels with similar burn-in risk from static content. The C6 is newer and will keep app and security updates far longer, so it stays useful longer.

Does the older LG support Dolby Vision?

Its listing says HDR10 only, though LG's older OLED marketing mentioned Dolby Vision. Treat HDR10 as the safe assumption and check the exact model before buying.

Can I watch Netflix and YouTube on both?

Yes. Both list Netflix; the C6 adds Prime Video and Disney+ and gets new apps through webOS 26. The older webOS 3.0 app selection is limited.

Which is better in a bright room?

The C6. Its evo panel with Brightness Booster fights glare better. Both are glossy OLEDs, so either benefits from curtains or bias lighting.

LG C6 65" OLED evo TV vs LG 65" 4K OLED Smart TV

Buy the C6 (A) for almost everyone. It is the newer set: four HDMI 2.1 ports, a brighter evo panel, the Alpha 11 Gen3 processor, 165Hz VRR, Dolby Vision and Atmos, and current webOS. The older LG OLED (B) is a curved 3D-era model with three HDMI ports, HDR10 only and webOS 3.0; its 4.4 rating from 228 owners reflects a good picture but dated software. Only pick B if you specifically want a curved screen or 3D playback.

Choose the LG C6 if you want the best current OLED picture, four HDMI 2.1 ports for consoles and PC, and long software support.
Choose the older LG OLED if you want a curved screen or 3D movies and do not need the latest gaming ports or apps.

Prices

LG C6 65" OLED evo TV: $1,186.00 at Greentoe (checked today)
LG 65" 4K OLED Smart TV: $1,399.99 at Walmart (checked today)
Difference: the LG C6 65" OLED evo TV is $213.99 cheaper than the LG 65" 4K OLED Smart TV today