SharePoint Online Person Validation via Workflow

Question

I have a custom list in SharePoint Online where a Person column is a mandatory field based on the value of another column. I understand this kind of validation logic is performed at the list level though the issue is that the Person column cannot be used in the validation.

In a similar question the suggested answer states that a workflow could be used. Person Group type column not listed on a custom list's Validation Settings page

I have tried this but the validation fails when I click save likely because the workflow hasn't executed yet. Is this even possible?

My workflow Sets the value of another column in my list and then ends, I have this workflow to start automatically when an item is created/changed.

Answer 1

A workflow is work which follows after happening of a specific event. So It is too trivial that no matter what logic you write in the workflow, it will start only after the 'Save Item' event happens in your case. Prior to this 'Save Item' , workflow won't initiate even if you set it to start automatically on item changed.