Thanks for this. By the way, I am making the assumption that your Partner Name field is a text field, so I am answering with that in mind. (You would have had less issue had you made this a dropdown field, but I can't really speak for what's allowable in your workflows.)
Your report filter above, is a combination of 4 separate filters. Each one searches independently of each other. As you can probably intuitively see, this works great if you are looking for SOMETHING.
e.g. in a Fruit Report:
Filter 1: look for apples. OR
Filter 2: look for pears. OR
Filter 3: look for grapes. OR
Filter 4: look for bananas.
Each filter executes in turn, and pulls in apples, pears, grapes and bananas. (not a perfect explanation but here you go)
But now, you're asking for the opposite and your filter set is being built as follows.
Filter 1: No apples. OR
Filter 2: No pears. OR
Filter 3: No grapes. OR
Filter 4: No bananas.
As you can hopefully intuitively see, each filter will execute in turn. Filter 1 will bring in pears, grapes and bananas. Filter 2 will bring in apples, grapes and bananas. Filter 3 will bring in apples, pears and bananas. Filter 4 will bring in apples, pears and grapes. Add oxford commas throughout.
I'm going to suggest a solution to you but I'm going to leave it to you to test and then report back if it works.
First: read up on "AND" statements, for example:
https://experienceleaguecommunities.adobe.com/t5/workfront-questions/filter-not-blank-and-not-x/m-p/478569#M11398
I think/hope this will end up being the answer to your problem. You need to filter with ANDs instead of ORs. i.e. one filter that says no apples, pears, grapes, AND bananas.
Your experiment would end up looking like this (who knows if this actually works... you'll have to test it out):
DE:Partner Name=Brand & Agency
DE:Partner Name_Mod=cine
AND:1:DE:Partner Name=pears
AND:1:DE:Partner Name_Mod=cine
AND:2:DE:Partner Name=grapes
AND:2:DE:Partner Name_Mod=cine
AND:3:DE:Partner Name=bananas
AND:3:DE:Partner Name_Mod=cine
groupID=4e8cbba6002547e9b75ef2bbd8cbb7b0
groupID_Mod=in
status=CUR
status_Mod=in
If this does work, remember to leave it in text mode. It will NOT convert back to standard.