I proposed map() because I deduced the possibility of multiple tags in same file/note. And the result is a list (with one or more values). And, by default, file.tags or file.etags is an array.
But you can try this (convert the output as a string):
TABLE string(map(file.etags, (t) => split(t, "/")[length(split(t, "/")) - 1])) AS tags
...