Strange residue on unused shower bought at auction- how do I get rid of it?

[Zengagoddess]

I desperately need advice.
We bought an unused shower with enclosure second hand. It had been in a farm shed In a damp and windy place for years after being bought at auction
by current seller. When we opened up the box, the shower glass was coated with tough white residue-? Cement dust ? Lime ? ?special coating gone wrong?
What could it be and how do I get rid of it? Can I get rid of it.?So far have tried various glass cleaners, kitchen degreaser , kitchen degreaser with vinegar, neat vinegar, white spirit, dishwasher tablet dissolved in hot water, micro fibre cloth, nylon brush. I’m exhausted but there a still patches like limes scale even though it’s definitely never been used.
Should I just give up and get another shower enclosure?

Razor blade?
Dh used to use a blade (comes in a pack from the hardware store) When he helped his friend clean the glass screens on showers in his rental properties, you hold it at an angle and gently remove limescale buildup.

Have you tried citric acid? Best thing for limescale. Cheap and readily available.

We’re coming to the conclusion that this is some sort of easy clean coating that’s degenerated over time (probably 20-25 year). I’ve just applied a product called baufix silicon remover and it seemed to have some effect.
I will give the critic acid a go but as we remove it with scrubbing, the surface is starting to look less and less like straightforward glass.

An update on the opaque unused shower enclosure.
We’re fairly confident now that the opacity is due to some sort of stay clean coating put on by the manufacturer. After 6 hours of hard elbow grease, the enclosure still has many patchy streaky irregular opacities , some as large as 15cm. The best products were baufix silicon remover with green nylon sponges as abrasives, possibly also Surgical spirits with nylon scrubber. It’s ok for family use but won’t make a good impression for Airbnb guests which was why we changed it in the first place.
Who would have thought glass could perish? Glass-really??? I’m sure that there is glass from the middle ages still working perfectly in big cold churches.
But if there is anyone out there who knows how to get rid of this coating, please come to our rescue? I’m thinking acetone?...Is this a case for piglet John?

Don't know if this helps @Zengagoddess, but if you go to www.balconette.co.uk/self-cleaning-glass/homepage, they have an article about self cleaning glass and also sell a dual sachet product. 1 sachet for cleaning and the 2nd sachet for recoating. It looks as if the cleaning product is alcohol based, so that maybe would help remove yours. It doesn't look to be particularly cheap though, depending on how much you would need. I have no connection with this company nor any experience of self cleaning glass. Good luck.

Update for what it’s worth. The final outcome was that I gave up and bought a new shower screen, repurposing the still slightly cloudy screens as a garden cold frame. I think glass that looks smooth to naked eye has micropores of some sort.