Can't Make Sense of Why OP_CHECKSIG Fails Here
OP_CHECKSIG needs to have the whole transaction to hash and to verify the tx. Btcdeb has the feature of allowing the tx as an argument however the website you linked doesn't hence this opcode is doomed to fail every time on this website.
It is reasonable to expect supplying the signature to verify the script/tx because otherwise to steal his coins, I would be able to copy one of his signatures and put them in my transactions.
Therefore I do suggest downloading and using the complete btcdeb.