Look Into

Smart FPS Booster is a client-side Minecraft utility mod that helps manage performance by applying configurable optimization profiles and dynamically adjusting selected settings.

Better performance for low-end PCs, potato PCs. Possibly on mobile, and also on some mid- or high-end PCs

Worldthreader speeds up servers by safely running each dimension on a separate thread.

Keep your server always online even if Mojang is offline!