Custom Fields defaultValue - UI default only?

Your software
My Mautic version is: 4.4.1
My PHP version is: 7.4…x
My Database type and version is: Mysql 8.x

Your problem
Custom Fields have a “Default value” property (defaultValue in the REST API).

Is the default value supposed to be applied:

  1. Only in the UI for setting the opening selected value on Mautic new contact form fields?

  2. Or also to new contacts created via the API for whom this field was not explicitly set?

  3. Or something else?

What I have tried
From my testing via api/ui I think its only for the UI but I want to check that’s the intended functionality here.

thx in advance Mautic Community!