WOW

Hi shkabuzar ,

I created a sample pbix file(see attachment) for you, please check whether that is what you want. You can create a measure as below:

last week = 
CALCULATE (
    SUM ( 'Table'[Count] ),
    FILTER (
        ALLSELECTED ( 'Table' ),
        'Table'[Date time]
            = SELECTEDVALUE ( 'Table'[Date time] ) - 7
    )
)

If the above one can't help you get the desired result, please provide more sample data in your tables (exclude sensitive data) with Text format and your expected result with backend logic and special examples. It is better if you can share a simplified pbix file. You can refer the following link to upload the file to the community. Thank you.

How to upload PBI in Community

Best Regards