Client-side FPS saver , caps your frame rate to 30 FPS while the Minecraft window is in the background, then restores your limit. Less heat and GPU load while alt-tabbed.
Sleepframe Unfocus Limiter is a lightweight client-side Forge mod for Minecraft 1.20.1 that caps your FPS at 30 while the game window is in the background.
What it does
Frame rate limit lowered to 30 when the window loses focus
Your previous limit is restored when you come back
What it does not do It does not rewrite the renderer and it does not use mixins. It only changes standard video options that already exist in the game, so the gain depends on your hardware and on what is really slowing your game down. It adds no blocks, items or entities, and it never touches your worlds or saves.
How it works It watches the window focus every tick and swaps the frame rate limit option. You can still change any option by hand in Video Settings afterwards. It works silently, with no message.