Drupal 9 Dropdown list Profile fields. "Select One" as default value on required field - forces user to complete

For select list/ drop down lists.  You may have run into the problem that you need it required and it has a default value that may be overlooked causing a break in data integrity.  

in your dropdown allowed values do this

|Select One
Value1|Value 1
Value2| Value 2

Set your default to the "Select One" which is technically a "Null" value since there isn't a key before the pipe "|".  This causes the validation message to fire. :)