I wanted to add for example the folder “b:\backup” to the exclusions list.
I guess the main problem is (was) that I did not realize that the b:\ drive, although it is a NTS formatted USB drive, does not appear under the list of NTS drives at all.
I have included it now with a Custom index location…
My problem is solved. But perhaps there is still the very minor issue why Listary does not recognice an NTFS disk at b: