Currently there is a limitation of Custom Dropdown fields at the Epic level up to 3 customs fields.

We would like to have more custom fields to be used at Epic Level.

Screenshot for ref.:

Jira Align Documentation for reference:

https://help.jiraalign.com/hc/en-us/articles/360041832653-Configure-default-and-custom-fields

Supported field types

Each work item type supports a number of different custom fields:

• Custom Text Input – Up to 2 fields
  • A small text entry box, intended for words or short phrases. 
• Custom Dropdown – Up to 3 fields
  • A dropdown list of choices, where one selection can be made. 
• Custom Text Area – 1 field allowed
  • A larger text entry box with some Rich-Text Formatting abilities, intended for paragraphs.
• Custom Multi Dropdown – Up to 2 fields
  • A dropdown list of choices, where one or more selections can be made.