How do your add a new task filter
Please tell me - are you referring to our mobile apps? If so - are you using the Android or the iOS app.
Adding filters in these apps can be done by going to the filters tab, then Manage filters (at the bottom) and "Add filter".
In this case, please tap on the filter tab, then "Manage filters" (at the bottom) and "Add filter". Afterwards, tap "Done".