Input lag should be less than 20ms if you plan to game on it.
If you're looking at an OLED tv for gaming, you should be looking at LG. Specifically the LG CX which has four HDMI 2.1 slots for 4K/120hz.
If you're going for Samsung QLED, you may as well go for the Samsung Q80T, which comes with one HDMI 2.1 slot, but doesn't carry the risk of OLED burn-in (not too much of a problem if you're only gaming casually).
May be a bit more expensive, but when you're already spending that kind of money, you may as well go for the best value.
EDIT: I'll also mention that outside all the key features like HDR, VRR, low input latency etc., they both also support AMD Freesync, but only the LG supports Nvidia G-Sync. Only matters if you plan to hook a PC up to it at some point. And even then, not a huge deal.
