Raymond Smullyan has several works, including several books, that explore diverse generalizations of the kind of fixed-points that your question is about.
Run the following search on MathSciNet: ti:(self-reference) au:(smullyan)
You will find the works I am talking about (8 in all). Perhaps the main one is:
- Smullyan, Raymond M., Diagonalization and self-reference, Oxford Logic Guides. 27. Oxford: Clarendon Press. xv, 396 p. (1994). ZBL0810.03001.
I am not sure if your exact fixed-point result is in there, but he has many very general fixed points of a similar nature.
Let me also mention that I have a short elementary note on self-reference results that I have usedwrote for use in some graduate seminars, A review of the Gödel fixed-point lemma with generalizations and applications, where I discuss the double fixed point and larger fixed-point systems, along with several applications, including the universal algorithm and other such results. Some of the fixed-point results are simpler than yours and you may know of them already, but the applications are interesting and other readers may find the presentation useful.