I'm not sure what it would take to convince me that sex is a spectrum.
It's really a matter of stipulative definitions, of by definition. From Merriam-Webster:
by definition idiom
: because of what something or someone is : according to the definition of a word that is being used to describe someone or something
A volunteer by definition is not paid.
A glider is by definition an aircraft with no engine.
What would it take to "convince" you that gliders are aircraft with no engines?
Same thing with the definition for sex - from Lexico:
sex (noun): Either of the two main categories (male and female) into which humans and most other living things are divided on the basis of their reproductive functions.
They don't say there, but their definitions for "male" and "female" make it clear that the "reproductive functions" in question are being able to produce, on a regular basis, sperm or ova.
I've seen the Quigley scaleWP and that convinces me that genital morphology is indeed a spectrum ...
There are probably hundreds if not thousands or even millions of "sexually dimorphic traits" that are "continuous variables" - height is the classic, paradigmatic case, but there are many others. But none of them justify any assertion or claim that sex itself is a spectrum, much less "bimodal" which seems to qualify as a category error.
But we could say that each different human karyotype was a separate sex in which case we could say that sex was a discrete spectrum. But it would be inconsistent with the Lexico definition for "sex" since there are still only two "reproductive functions" - i.e., producing two different types of gametes.
Since these individuals have to contribute different sex cells (oocytes and spermatozoa in our species) I'd say the process of sexual reproduction is rooted in a binary at the gamete level.
The previously mentioned article on Gamete competition, gamete limitation, and the evolution of the two sexes at the Oxford Journal of Molecular Human Reproduction by biologists Parker and Lehtonen seems the classic work on that topic.
