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.

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.