If you are just trying to avoid collections that have less than a certain number of books, then you can set this up when you customise the Kindle Collections plug-in in Calibre - just put, for example, 2 in the ‘Minimum’ column & then when you ‘Create Authors’ you’ll only get collections for those authors with more than 2 books in your library.
If however you also want to get a collection that holds all those authors with, say less than 2 books, I’m trying to think of a way to do that… there might be a simple way but only thing I can think of at the moment is to try the Author Book Count plugin at
https://www.mobileread.com/forums/sh...d.php?t=241441
(I haven’t used this, by the way, so can’t comment on how it works).
Then you can sort by that column, select all the authors with 1 & 2 book authors, give them a new tag, & then create a collection based on that tag.
Apologies if I’ve misunderstood what you’re trying to do. And of course, someone might have a much easier way to deal with your problem, but I have a cracker of a headache at the moment & this is the best I can think of at the moment.
Good luck!