Searching image exif data in app on Dropbox Professional plan

I save all my photos to Dropbox. They have lots of exif information; location, tags, keywords, captions etc, written from various programs, nowdays it's Digikam. I try and give the photos meaningful filenames as this is rapidly searchable across platforms, but most of the good information is stored internally in the files themselves.

I was interested to see that the Plus plan introduced searchable files, but not jpegs. But from my understanding the Professional plan does allow text searches inside image files. This is so useful to me I've upgraded from Plus to Professional.

However I'm not sure I've understood correctly. The Help page says:

"You can search images in your Dropbox account based on the content in them. For example, you can search for “clothing” to see all images of clothing (and images related to clothing) in your Dropbox account—even if “clothing” isn’t in the file name."

I would understand this to mean I could search any of the exif data from within the IOS app but my initial experiments in the app and on the website have not been successful.

For example, the image: https://www.dropbox.com/s/npdks5bmaq7k4pv/Sun%2017%20Nov%202019%2016-42-10%20GMT.jpg?dl=0

contains the Caption 'Lumiere 2019 - Cathedral" in the Caption Abstract and Comment fields (output from exiftool):

Caption-Abstract : Lumiere 2019 - Cathedral
Comment : Lumiere 2019 - Cathedral

but I've had no success searching on these text strings.

Does the internal image search not work in the way I'm assuming?

I've been charged pro-rata for the Professional plan until end December but I'm thinking of downgrading back to Plus so I don't get the full-year charge for 2020 as I'm not convinced Professional actually does what I'd hoped.

Dougie