Best way to indicate required vs optional fields

Question

I'm having some issues deciding how to indicate to users the some fields are required and some are optional. I've encountered these three scenarios, and the following solutions:

1. All fields are required --> I could add a text that says "all fields are required".
2. Some fields are required --> If most fields are required, I would add the word "optional" next to the fields that are optional. If most fields are optional, I'd add a "*" next to the required fields.
3. All fields are optional --> I'm not sure how to treat this case.

My team's concern is that if we write "All fields are required", then users might expect to have some guidance in every form (when fields are not all required).

Here's a lo-fi wireframe of a table form:

Answer 1

If users can be faced with the 3 scenarios I would consider using a single pattern for all of them:

At the beginning of each form always show a message that says "Required fields are marked with an asterisk (*)"

Then always mark required fields with a * and never mark any optional field.

This rule would apply to all forms.