To make tagging easier, you can switch to the “Filter mode“.
Click with the right mouse button on one of the tag-categories and select “Switch to ‘Assign Tags’ mode“.
The Catalog Tags panel turns then to the view as shown on the left figure.
Instead of the previously displayed circles, you will now see square check boxes right behind the tag categories.
This delivers you from dragging elements onto the tags and allows you to select the elements in the browser and assign them to the tags by simply clicking on the respective checkboxes.
Such assigned tags will be displayed with a checkmark.