If you want to apply conditional validation on 'Image Data Uri' or 'Audio Data Uri', then you need to add 'Scheme' input as 'DataUri'
{{userForm.controls?.scheme?.errors?.dataUri.message}}
If you want to apply conditional validation on 'Audio Data Uri' then you need to add 'Scheme' input as 'DataUri'.
Conditional Expression with type 'string'
{{userForm.controls?.audioDataUri?.errors?.dataUri.message}}