Find Activities not working in 5.19beta1 and master
It's working in 5.18.4. In 5.19+ it just always returns all activities.
It's because of a change in CRM_Core_Form_Search::setFormValues(). This now calls $this->getFormValues(), but for activity search all that does is return NULL, so no form values get set.
To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information