Can a Coin with High Difficulty Still Be Vulnerable to Other Types of Attacks?

Yes, high mining difficulty primarily protects against 51% double-spending attacks. However, a coin can still be vulnerable to other attacks.

These include smart contract exploits (if applicable), denial-of-service (DoS) attacks on nodes, wallet software vulnerabilities, or economic attacks like 'exchange stuffing' or market manipulation. Security is multi-layered and difficulty is only one defense.