Valve index HMD dynamic / manual resolution?

I know each eye is 1440x1600 but does it dynamically scale down if it runs a more demanding game or if the graphic card is not powerful enough? Or can you manually configure the HMD resolution to 1080p instead? Is this what's meant by under-sampling?

Also can the refresh rate be configured lower than 80Hz? If not then it's just Steam Motion Smoothing?

Sorry if my questions appear dummy and I completely understand the experience on weaker systems is not enjoyable, but I am purely interested in understanding how VR and this HMD works when minimum requirements are not met, and I am already planning to upgrade my PC this year anyway.

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