Hi Sierra,
Thanks for asking! HDMI 2.1 is a somewhat complicated specification, so to better help our customers with their TV decision-making, we highlight the specific features supported by each TV model. All 4 HDMI ports on the S90D are capable of Auto Low Latency Mode (ALLM), Dynamic Metadata (HDR10+), Variable Refresh Rate (VRR), and 4K@120Hz (up to 144Hz for PCs). eARC support can further be found in HDMI port 3.
~Samsung Advisor