Hi,

Add required attribute on your field.

Example:

<field name="your_field_name" required="state in ['progress']"/>

But this will effect only on UI level.

For validation, you must enforce server-side validation in Python.

Use either a method override (e.g., button logic) or @api.constrains.

  @api.constrains('state', 'your_field')
    def _check_required_field_on_in_progress(self):
        for rec in self:
            if rec.state == 'progress' and not rec.your_field:
                raise ValidationError(_("The field 'Your Field' is required in 'In Progress' state."))