What are the Performance-killer for VR(eg.OculusQuest2)? all postprocess, all screen-space?

[gpu2015 (anonymous_user_a588e7a6)]

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DisplacementMap in VR?
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paticle system in VR?
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and do you know when should i change the default display refresh rate of Quest2?
https://forums.unrealengine.com/t/need-to-change-display-refresh-rate-for-quest2-while-dev-game/249148

Thanks!