1. If it is a record creation specific Quick Action, check the following:

a. Make sure the user have edit access to the record.

b. Make sure the user’s profile have Read and Edit Field Level Permission to Parent field. 

c. Check the whether the user’s profile have access to the Record Type selected.

 

2.  If Quick Actions on Cases and Work Orders are not visible, then kindly check https://www.infallibletechie.com/2018/12/quick-actions-on-cases-and-work-orders.html.

3. Check the page layout assignment and confirm whether it is added to the assigned page layout.

4. If Dynamic Actions are used, then edit the Lightning Record Page, check the Highlight Panel Component and confirm whether the quick action is hidden with condition.