This is the second time I see a forum post of this kind where this xdg-portal dialog pops up but it’s not aware of what application this is triggering.
So far I don’t know any logfile where this event would appear in. If the dialog knows what app triggered this, it will display its name of course. I have absolutely no idea why it would not be aware which app requested it and I hope this can be improved upon at some point.
Now the “Remote control requested” dialog will always tell you what is requesting remote control; at the very minimum, it will now give you the technical ID of the thing making the request if it can’t display a pretty name — rather than displaying nothing. (Stephan Seitz, link)