Detect external sidecar modification

Hello,

I am new to Digikam. I am trying to configure it so that it works together
with another application (Immich in my case).

I have configured it to  read from and write to sidecar files. Also, I have
checked "Scan for new items at startup", but not "Fast Scan".

As I understand it, the program should detect externally modified files
upon startup. Does this also apply if only the sidecar file has been
changed, but not the actual image file? What if a previously non-existent
sidecar has been added externally?

In my experiments this was not recognized. Is there a way to make it work?

I am grateful for any comments and suggestions.

Best regards
Daniel