In its manual it says Spectralayers can be used by going to the directory path it shows, and choosing spectralayers.exe. . I went to as fasr as the Win64 but there are no files showing there. but when I look at Resolve plug-ins, it is checked.
However when I try the next step of going to the clip and choosing the plug-in, not there.
It’s there, otherwise you would not be able to run SpectraLayers at all.
For some reason your file explorer is hiding it ?
What do you see when you right-click on SpectraLayers 11 icon > Properties ?
Rob got some answers over there in the BMD forum:
https://forum.blackmagicdesign.com/viewtopic.php?f=21&t=215121
Might be helpful for others ending up here looking for the same.