This page isn’t working – activate theme: full wordpress crash

This page isn’t working **** is currently unable to handle this request.
HTTP ERROR 500

This is the Error what comes when I try to activate the Blackfyre theme. The hole WordPress isn’t working anymore after that and I need to reinstall it fully.

Someone maybe help me? Im Using 5.1.1 WordPress (because Blackfyre Version is 5.1.x – information from themeforest) running on CPanel/CENTOS 7.6.

All other themes have no problems.