This is my one and only post on the Plex forums. I have been using Plex for many, many years.
This feature has been requested since at least 2014, see this thread: Change playback speed on photo slideshow
The lack of this feature makes the app-based photo slideshow (in my case, on Fire Stick) completely worthless. The photos change way too fast to be appreciated, and bigger photos don’t load at all during the 5 second dwell time.
I have started migrating my content to Kodi for this reason alone.
The fact that the feature is so basic, and the fact that the Plex team has gone on for so long without either acknowledging the issue or doing something about it has killed all my goodwill toward this product. I no longer want to support it.
Hopefully the developers will take this as a signal and improve their customer strategy. But once I’ve completed shifting my media library I don’t really see a reason to come back to Plex.