First of all, there is no direct translation. In each case you will need to translate it differently, depending on the context.
Wiki says :
Handwaving is a pejorative label applied to the action of displaying
the appearance of doing something, when actually doing little, or
Now, assuming you want such a meaning, you can use
"Создавать иллюзию деятельности" or "Создавать видимость деятельности" which literaly translates to "Create an appearance (or visibility) of action(or work)". A common phrase would also be "создавать видимость бурной деятельности". You can use this when you, for example, want to describe someone who is doing nothing at work, but tries to pretend he is working hard when his boss comes by:
"Он целый день сидел и создавал иллюзию бурной деятельности" >(literally)> For the whole day he was just sitting there and creating an appearance of hard work.
Now, for the debate. Wiki says:
Handwaving is also occasionally used in informal debate or discussion.
If the opponent in a debate uses the term, it is meant as a shorthand
way to accuse the proponent in the debate of having committed a
logical fallacy. In this sense, it is also as if a participant is
waving their hands to obscure clear debate, as a verbal or logical
The part about "smoke screen" is easy, you can say that the opponent is trying to "запутать", "создать дымовую завесу" (which would be a literal translation), or, if you want a colloquial form, "запудрить мозги".
As for the other parts of the wiki article, I can't really come with a short (or, possibly, one-word) translation for them.
As for your example:
If someone gives a derivation of a formula in math, physics, etc. without justifying the > steps, you can say in English that the person
is giving a "handwaving argument" or "this step is handwaving"
I suppose the meaning here is close to "unclear", "unobvious" or "ambiguous". In this case you can say "неочевидный", or "неясный" which is not a literal translation, but suits well f you are talking about, say, a math formula:
This step of the deduction is handwaving >> "Этот шаг доказательства