sorry but, hahahahahahasobsobsobsob , when do people actually learn..
why facebook.. too many cure cancer fb posts which caused more harm.

you can start by posting what you have just applied on ur windscreen.


personally, i just get 2-3 bunch of steel wool 0000 grade (very fine type- can catch fire fast)
then scrub ur whole windscreen clean.

watermark all will go away after a few pass.

then clean area good and top a coat of rainX or rain repellent.
(also clean the wiper blades properly, by taking it off and wash until no black marks)
rubber blades loves to leave residue which is why I dont use em.

please show what u applied.
if it etches ur glass, then no choice, need to special cut (polish) the glass.

2nd method i rarely do is use a glass scrapper and some detergent as lub.
glass scrapper will level any gunk to bare glass level with no scratch (if done properly)

for q1,
ace hardware for 0000 grade, I just go tesco (no grading), more or less same thinness haha.
so far used on toyota, peugeot, merc; no issues. (duno glass quality better than proton or what)
skill not need much just need elbow grease if big car.
just need wash window(/clay), dry it completely, then scrub whole glass (i sometimes pour alcohol to ease scrubbing) 3 finger pressure scrub, not palm scrub (only heavy residues i use palm).
vertical movement on glass

q2,
glass scrapper is usually used on glass cook tops and windows.
what it does is level off deposits stuck to glass by the blades.

need to use at correct angle to scrap or will just jump over dirt.
will not weaken as the glass hardness is higher than the blade.
blade must be correct or will scratch glass (hard to source window blades).
can remove tar, paint drops, and sticker residue
horizontal movement on glass

Sorry no, I do not provide these services.
I only explain what i done before here, never like meeting random people

and yes, show the product in pic and if got the ingredients better.
so other may know next time and can breakdown the chemicals.

Etch can also feel smooth.
what i worry is that the white substance went into the micro pores of the glass (by sand and stones).

and to people who said car body polish will ruin your window, nope.
if the body polish is so darn strong to scratch glass, bye bye for your paint.
glass is harder than paint.

and looks like someone here also have the same issue
https://forum.lowyat.net/topic/3864337/all

well looks like u got an etched glass.

the water mark remover (probably acidic) went into the light scratches/etching (by acid rain) on your glass and seeped into the laminated layer

and when it dries it leaves residues (cloudy).

because dirt(or dried up water mark acid) have went it, you pretty much have nothing else to do.

and since it's ruined, you could try taking a cloth and pouring some turpentine and let it soak before rinsing it off.
why? maybe the alkaline can neutralise the acid and bring it back out. no guarantee, but can at least try before replacement.

yeah any liquid/oil that contact the surface will make it smooth and reduce distortion of light hence disappear.
but it could also flow into the minor cracks/scratches.

here's an example.
stone chip ur car, first is small hole, no crack.
after driving 1 year, the elements (water, dust, dirt etc) settle and expand in the chip.
expansion and contraction will force a channel into the glass
with the different expansion character, a crack is developed or the marked area will very visible.
then the dr cermin will say 'left too long, dirt went in already'
then forever u will see the shiny mark.

In this case, im guessing the solution ate more rapidly and dried inside.
with water it will become clear, but evaporates quickly.
other solutions will dry slower so fog will be slower.

one way draw the foggy out lines in the inner side
then saturate the area with something and let dry.
see if foggy lines change.
if major (shape) change then means liquid went into the laminated areas
if minor (whiteness/ clarity) change then etching in the cracks

if TS cannot tahan, then better change glass.
but must make sure glass installed properly or water enter even more problem.

I cannot guarantee anything
since tried so many already and lazy try turpentine, just tukar, safer anyways.
just make sure insurance cukup to claim.

Water leak will only know during massive downpour, normal rain will not leak unless damm bad install.
but I know those cars with auto wipers, most kena messed up after replace windscreen
(just make sure they use new sensor with window, and not tear the sensor off old and paste it back on)