Wouldn’t car wax get your windows all greasy?
We used to use a window cleaner called AFAICR ‘Windowlene” It was a liquid applied with a cloth that dried to a white powder you just left it on till you were ready then polished it of with clean rag - Hey! Daylight and clean windows.
I still want to know why windows are soaped in the first place. To hide construction? Why? Do people think less of you because they can see you are improving your property? There was a time when they cut holes is construction barricades so that passersby could gawk at construction. I just don’t see it as a an eyesore. And does a little shmeer on the windows really block the view that well anyway? It not like it makes them completely opaque. What’s up with that?
You pretty much got all the answers in your other thread.
There is a Health & Safety stipulation (in the UK) for any glazing on a construction site to be marked with some form of manifestation to ensure no one walks / bumps into it. This is not restricted to the soap, but can be in the form of a taped cross or other distinctive marker, to ensure no one misses the glass. The soap seems to be the most common and simplest product to use (and remove), which will also provide a semblance of security for any expensive gear on site.