different jargon

I would say that not only is a plural form optional, it would be uncommon. I don't assert that it would be incorrect, only that i would be surprised to see it. So, for example, scientific jargon would include the jargon of chemists, of physicists, of geologists, of botanists, of zoologists, etc.

"Jargon" is used as a plural noun as it is.

You say the plural form is optional, but uncommon? I get confused because of the structure of your sentence:

-I would say that not only is a plural form optional, it would be uncommon.

because before seeing the comma, I would have expected to see something like:

-...not only is a plural form optional, XYZ is also optional.

There's nothing wrong with the sentence i wrote, so i don't really feel responsible for your confusion. The word "jargons" is both optional and uncommon. You could use it, although you don't need to use it (optional) and it is highly unlikely that a native speaker would use it (uncommon).

Thank you~