Calculated Column from another fact table without relationship

Hi DIACHROMA,

You may try this Measure.

Sales D+30? =
CALCULATE (
    COUNT ( Sales[OrderDate] ), //Count Order in the Range
    TREATAS ( VALUES ( 'Events Attendees'[Attendee] ), Sales[Customer] ),
    FILTER (
        'Calendar',
        'Calendar'[Dates] >= MINX ( 'Events Attendees', 'Events Attendees'[EVENT DATE] )
            && 'Calendar'[Dates] <= MINX ( 'Events Attendees', 'Events Attendees'[DAYS +30] )
    )
)

Then, the result will look like this.

Also, attached the pbix file as reference.

If this post helps, then please consider Accept it as the solution to help the other members find it more quickly. If I misunderstand your needs or you still have problems on it, please feel free to let me know. Thanks a lot!

Best Regards,

Community Support Team _ Caiyun