Ensure File > Project Settings > Video Rendering and Effects is set to "Mercury GPU Acceleration". To make this guide more useful, let me know:
Activate the stopwatch for a property to set keyframes. Adobe After Effects 2021 v18.4.1
Better visualization of what is slowing down your renders. 2. System Requirements (v18.x Era) OS: Windows 10 (64-bit) or macOS 10.15+. RAM: 16 GB minimum, 32 GB or more recommended. Ensure File > Project Settings > Video Rendering
Are you trying to install this specific version or troubleshooting a project in it? Adobe After Effects 2021 v18.4.1
Press Spacebar to RAM preview. Drop resolution to "Half" or "Quarter" if playback is slow.
Intel 6th Generation or newer/AMD Ryzen 1000 series or newer (AVX2 support required). 3. Essential Workflow