I searched but did not find any discussion of this.

Has anyone been able to send an SMS message with photo attachment via KDE Connect?

On my machine (Manjaro, Plasma, KDE) it just seems to abort the attempt. (Blanks message entry box and attachment is reset to nil.) No message is sent.

I thought there might be a file size limitation, but I tried a very tiny image and no luck.

But overall KDE Connect is SO awesome and I am very thankful for everyone's hard work!

SMS does not support attachments of pictures, for that you need MMS, which usually is an additional service of your provider.