can you post a pic from farther back, just for context? Is it just clear glass? Mirror? I've had really good luck removing water spots, minerals from windows, sinks, shower tile, etc. with this product.
https://bio-cleanproducts.com/collections/hard-water-stain-remover I was able to get a free sample from Ace Hardware; they may have smaller sizes, too, for less $. You might be able to get a sample from the company, too. There is another product with a similar name; make sure it's this one. It's also available on Amazon. Good luck!

Yes it is clear glass - but mirrored (mirror) as you can see from pic..oh thanks so much...its def not outside..but inside the glass...very strange one indeed..i will try the website

Thanks again for your help!