When you navigate a show in Kodi it has “All Seasons”, “Specials”, “Season 1”, etc. and if you select “All Seasons” it will merge specials within the episode order where appropriate so you can watch movies, recaps, etc. in the order it should be watched.
Not available as a “one-off button”…
But there’s 2 use cases:
If you play a series, Plex will present the next episode at the end of each episode. This goes by airdate so specials will be threaded in at their respective slots (e.g. between seasons, holidays…).
you can set the show to hide seasons in the show’s advanced settings and apply oldest first ordering… this will present you a sequential list of all episodes and specials as they aired.
Not super convenient but possible
Thanks @tom80H . I appreciate the suggestions however, that would would not work for anime as often times the official watch order is different from the airdate. In my example, S00E01 occurs between S01E02 and S01E03. Season 1 aired 2012 whereas the special aired 2014. I hope to see this feature in a future iteration!