Not sure why but it seems there is no Select All button but there is a Deselect All button. Not sure why a Select All wasn’t added when the Deselect All was added. It would be nice to have this so that if you, for example, upload a big folder of TV shows to our Plex Server and we have already watched the shows we can easily Select All and set them all to Watched.
Here is where I am talking about adding the Select All button.
I thought that was odd too, but there is an alternative. After selecting one item, if you hold down the shift key while selecting a second item, all of the items in between will be selected.