Collections filters seem to work in calendar reports, so I recommend you try there. The article link is here:
https://experienceleague.adobe.com/en/docs/workfront/using/reporting/reports/text-mode/reference-collections-report
Some sample code shown below -- I recommend testing it before use and adding/amending it as needed.
assignments:assignedToID=$$USER.ID
assignments:assignedToID_Mod=in
assignments:status=AA AD
assignments:status_Mod=in
Please note -- this kind of filter is something you would have gotten from an assignments report in standard mode. Then you just flip it to text mode, copy/paste it into your calendar report, and append each line with “assignments:”. You can do the opposite of this -- copy and remove all the “assignments:” text and then paste the remainder into an assignment report and convert back to standard mode, to see which fields I used.