I recommend (like Madalyn) you transfer over to using an assignment report rather than a task report. The assignment report allows you to filter on specific assignments where the assignment's status is not "Done" and the assigned to ID = your wildcard. It's not possible to pull a specific assignment status from a task report using the wysiwyg (standard) mode otherwise.
If determined to stay with task report, the following text mode is one option that might work for you -- provided your other filters are not too many/complicated. In summary, the codeblock says "hey, look at all the assignments on each task and if it's assigned to the user, AND the user is not done, let me know"
EXISTS:a:$$EXISTSMOD=NOTEXISTS
EXISTS:a:$$OBJCODE=ASSGN
EXISTS:a:taskID=FIELD:ID
EXISTS:a:status=DN
EXISTS:a:assignedToID=$$USER.ID
You'll add this codeblock to your existing task report filters by changing the filter section over to text mode, and inserting this text at the end of the code that you see. If you see any lines prefaced with "OR:1:" (etc.), you're seeing complication, and you can try adding a second copy of the codeblock above and preface the lines with OR:1: as well. (This stuff kind of slows down your report and eventually you'll reach a limit and the report will error out on you)
I hope it's pretty clear to you that your pre-existing task filters are things like "I'm only interested in tasks that are not complete, and only if the project status is active" -- these filters are pretty standard and easy to set up with the standard mode, so you should always set them up first before pushing on with the text mode that people give you.
To read up on EXISTS statements, including how to tell when you need to create one, use this link:
https://experienceleague.adobe.com/docs/workfront/using/reporting/reports/text-mode/create-complex-text-mode-filters-using-exists-statements.html?lang=en
