Good question. I should have been clearer!
Using the mouse, I cannot select a formatting tag in the editor (when I'm creating a custom slide). I thought that was the (only) way to select formatting tags.
Just now, I went to take some screenshots to illustrate what I meant and I made a discovery. Once I have right-clicked or command-clicked on the text that I want to format, that brings me to, amongst other things, the formatting tags. That's where I expected to use the mouse to select the tag(s) I want to use. But my discovery is that I use the arrow keys to move up and down the list and then press return to put the formatting tag into action.
I don't remember it being that way in previous versions. But, for various reasons, I wasn't a frequent user of the formatting tags, so it's more than possible that I don't remember correctly.
I'll be interested in what really used to happen, and what the intended manner for putting these tags into action is.