TWO OPTIONS:

Via the Window Action:

Add this to the Window Action context:

{'default_x_studio_date': context_today()}

This is normally used in Odoo to support filters in Search Views, where it needs to be converted by adding .strftime('%Y-%m-%d') but works just fine in Window Actions as I have shown.

Via a calculated field:

1. Click MORE at the bottom of the Field Properties tab.

2. Enter this code in the COMPUTE field for DATE:

Note that x_studio_field_IFERO was the name of the custom date field I added, yours will be different.

3. Enter this code in the COMPUTE field for USER.

Note that x_studio_field_aMyLf was the name of the custom one2many field (res.users) I added, yours will be different.