Limiting Display Frame Rate to Lower
There doesn't seem to be a way at this time.
So far, all I know is a hidden feature in Android S Preview Revision 3, namely Game Optimization in the Game menu which can lower frame rates, such as Xperia STAMINA mode.

Portal: Android 12 DP3 Analysis: Here are all the hidden features! | xda-developers.com
Screenshot: 17-Game-Mode-2.jpg (563×1155) | xda-developers.com
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