Hi @Peppearson ,
You can refer the following threads to get it by using ROW function:
Add new row with accumulate in Matrix
Looking for difference between two values by filters
If the above one can't help you get the desired result, please provide some 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
Community Support Team _ Rena
If this post helps, then please consider Accept it as the solution to help the other members find it more quickly.