Hmm, well, Ivan Coyote published most of their books while they IDed as a butch lesbian, but now IDs as non-binary. (And their books are all amazing.) I especially recommend Gender Failure, which is written with another non-binary author(/musician), Rae Spoon (review here). 

Freak of Nurture by Kelli Dunham talks about the author’s genderqueer lesbian identity (review).

Other non-binary books that are sometimes categorized as sapphic or have been reviewed at the Lesbrary:

• Orlando by Virginia Woolf (review)
  
• Written on the Body by Jeanette Winterson (gender unspecified)
  
• Lost Boi by Sassafras Lowrey (review)
  
• A + E 4ever by i. merey
  
• Out of Salem by Hal Schrieve (review)
• First Spring Grass Fire by Rae Spoon (review)
• Stone Butch Blues by Leslie Feinberg
  

Sapphic books with non-binary love interests:

• Girl Made of Stars by Ashley Herring Blake (review)
  
• The Little Homo Sapiens Scientist by S.L. Huang (review)
  
• Mermaid in Chelsea Creek by Michelle Tea
• The Brilliant Death by Amy Rose Capetta (demigirl MC and genderfluid LI)
• Once and Future by Amy Rose Capetta
• Like Water by Rebecca Podos
  
• The Brightsiders by Jen Wilde (review)
• Heart of the Liliko'i by Dena Hankins

A Lake of Feathers and Moonbeams by Dax Murray has both sapphic main characters and a non-binary main character (review).

I know The Lost Coast by Amy Rose Capetta has a prominent non-binary character and sapphic representation, but I don’t know the particulars.

There’s also a goodreads list of Non-Binary (Genderqueer, Genderfluid, Gender-Unspecified, etc) Fiction and Memoirs that may be helpful for you.

I hope that helps!