When inserting a blu-ray disc, even though there is a device action designed to trigger the command "vlc bluray://%d", the action is not triggered and so KDE does not suggest playing with VLC when inserted. This seems to hinge on the value "Available Content" not containing the default text "VideoBluRay". By contrast, the actions that cause VLC to be suggested when inserting an audio disc or DVD work fine.
This action actually comes from VLC itself; you'll need to report it to them so they can fix it.
Created attachment 158267 [details] Screenshot of issue
VLC devs have confirmed that the text is correct but isn't triggering the action, here: https://code.videolan.org/videolan/vlc/-/issues/27869 This only seems to affect BluRay discs.
Thanks for following up!