Problem with my theme

Hi all,
I am currently using and playing a great theme made by KBDesign https://kbdesign.bdl.pl/gridfolio-free-wordpress-theme/

I was making different Pages templates based on the original one but I think I messed up something since I can’t open my posts anymore (see : https://www.compmonks.com/compmonks/works/)

Any idea how I can debug this?
Thanks
All the best