UPDATE:
After Effects 2019 (v 16.x.x) isn't compatible with macOS Big Sur.
Big Sur has some major code changes under the hood. After Effects interacts with certain components of macOS that have been modified or no longer exist in Big Sur resulting in incompatibility issues. Some users in this thread have reported that they are not running into this issue after updating their plugins. Based on that info, we recommend:
- Updating to the latest version of After Effects 2020 (v 17.5.1) if you're running macOS Big Sur
- Updating your plugins might also help in resolving the issue
Thanks.
Rameez