After Effects 2021 Crashes at startup

Hi RezMultimedia,

Sorry for your issue.

Could you share your system specifications (CPU, GPU, RAM, OS)? Also, did you install any third-party plug-in or script?

Try resetting the preferences of After Effects and see if it helps: https://community.adobe.com/t5/after-effects/faq-how-to-reset-trash-preferences-in-after-effects/td-p/10634342 

Let us know how it goes.

Thanks,

Nishu