Did you ever encounter a requirement to create a Quick Action on Entitlement, but wondered why can’t you see the option to create one on the object?
Well, the reason why you don’t see the quick action option is that, Entitlement doesn’t support lightning yet.
“Entitlements are only supported in experiences built using Salesforce Tabs + Visualforce and can’t be added to Lightning Experience.”
As a workaround for quick action, create a custom button or link on Entitlement, use visual force page or Lightning App Builder URL to open either Aura/LWC from Entitlement.