(note the missing c:\ prefix)
Can you do that?
Best I can tell is that the c:\ is needed, a full path to the folder is needed (in the Include only: dialog).
To me, seems that c:\users\admin\nextcloud should be working?
Other then in Indexes -> NTFS, do you have other items in the other entries under Indexes that may be adding back in what is not included in your NTFS:C: setting?
Is there anything "special" with the "nextcloud" directory?
As a test, set up a new "Profile", using a separate instance that you start (initially) with the -no-auto-include switch, & then set C: to be included, but have it Include only: some temporary directory, say, C:\ionlywantfiles.dirs.includedhere\.
With that, does it not only see files/directories within C:\ionlywantfiles.dirs.includedhere\ ?
Oh, & you're on Everything 1.4.
I wonder if that matters?
Nope. It should be the same.
In your 2nd shot above, here
viewtopic.php?p=70604#p70604, it looks like you Excluded: nextcloud (maybe).
(It says, Exclude
folders: & you have "file:" include there, & while you may be able to put something that ends up making the request invalid, I believe, in that case, it shouldn't really be affecting thing.)
Be sure to remove that entry, & add C:\ to the nextcloud entry in Include only:.