do you by chance know about any tool that can use "content" from images metadata to show up in the slideshow, somehow like I use it in mine (like f.i. here
- click on any image to start it)?
I doubt that is possible with "USB stick only", because that would require the smart-TV's own slideshow application to be able to display image meta data ... which is doubtful. If you have a computer/Mac connected, there might be an application ... If the TV has "Google TV" or "Android TV", there might exist an app in play.google.com/store that has capabilities to display captions from exif/iptc.
In reality, I think you will have to connect a computer to the screen if you want to display captions. Or the TV would have to be a "smart TV Android/Google" with internet, which should provide some alternatives. I can't imagine any better solutions with only USB stick and no internet.