Hello Nishant Patel,
Thank you for reaching out to us.
We kindly request that you navigate to Elementor > Settings > Features > Flexbox Container > change the value to “Active”, and try to import prebuild templates after that.
https://www.8theme.com/documentation/xstore/xstore-builders/new-xstore-header-builder-with-elementor/
Kind Regards,
8theme team