Did you use a scrubbing brush and try to remove mould by scrubbing, not just by spraying stuff onto it.?

I’ve never actually seen mould that colour. Is it something that is “IN” the glass or can you use a flat blade paint scraper to remove on the shower screen. And just heavy handed hard work with a scrubbing brush on the tiles. It looks like a chemical build up of some kind, not mould.

Is it this, not mould.

An orange or brown buildup on your shower screen is usually a combination of hard water minerals (specifically iron), soap scum, and bacteria. The reddish-orange color is often caused by iron in the water supply oxidizing when exposed to air, while the slimy texture indicates Serratia marcescens, a bacteria that thrives in moist environments.

Here is a guide to removing the buildup and preventing its return.
How to Clean the Buildup
The most effective way to remove this buildup is by using acids to dissolve the mineral deposits.
White Vinegar & Dish Soap (Best for General Buildup): Mix equal parts white vinegar and water in a spray bottle. Add a few drops of dish soap (like Dawn) to act as a binder. Spray generously on the glass, let it sit for 15–30 minutes, then scrub with a non-scratch sponge or magic eraser.
Baking Soda Paste (For Tough, Crusty Spots): Mix baking soda with a small amount of water to create a thick paste. Apply directly to the stubborn, orange, or brown, crusty spots, let it sit for 15–30 minutes, then scrub gently and rinse.
Lemon Juice (Natural Acid): Cut a lemon in half and apply it directly to the affected area, or use lemon juice in a spray bottle to break down mineral deposits.
Commercial Cleaners (For Severe Stains): If natural solutions fail, use products specifically designed to remove "Calcium, Lime, and Rust" (CLR)
Razor Blade (Last Resort): For extremely stubborn, raised crust, you can gently use a razor blade to scrape the residue off, but be careful not to scratch the glass.

Thank you very much dreamer I will consider all your advice appreciate your help and your informative details ,,,I will try to use paint scrapper and brush to see the result

Was there a repair at any stage? It’s hard to tell but has silicon or some type of sealant been used? If so it can trap mould and you won’t be able to remove it with surface treatments. You’ll need to remove the sealant and replace. If you’re an owner not a renter I’d price a replacement screen as those cleaners add up in price and the problem is
Iikely to reoccur.

Thx bigreader I am a renter not the owner,,,,, recently I rented the property and as per dreamer advice I just checked the shower and I realized that silicon has been used and its color changed to black ,,,,,that means old silicon has to be removed and apply new one.

Now question can old panel of the shower's screen for house built 1980 be two pieces of glasses and mould stuck between these two pieces ? as by touching the black area of the screen I feel like a normal glass I don't feel any roughness or layer of buildup and when I try to use painter scrapper nothing comes off ?

I think as a renter I’d call the tenants advice line for your state. Generally it’s part of consumer affairs. I think it is mould or similar and should be repaired/replaced by the landlord. Talk to the advice line and get their professional opinion and advice on the correct next steps.

Shower screens can have two sheets of glass laminated together, and the mould develops in the gap, which is a fraction of a millimetre wide. Nigh on impossible to remove.

Agree with bigreader’s comments above. If you can’t scrape the brown/orange substance off, then it would beneficial to contact your property manager and request a new shower screen.

Hopefully the owner or property manager took photos of property prior to you moving in. This issue with the shower screen should be noted, if it was already there prior to you moving in.

Thx bigreader and dreamer for your help

Thx Compass Kitchens for sharing your thought

Based of the advice of dreamer and bigreader what happened I am guessing : silicon seal deteriorated and leak happened and then mould built up between 2 sheets of the shower glass screen,,,,,because we I used the scrapper I can't remove any substance from the glass,,,,which that gives me indication that mould is between the two sheets of the glass

Unfortunately once it’s between the two sheets of glass it’s impossible to remove, your landlord may be able to replace the glass once he knows it’s mould. We had same problem and had to replace the shower screen because no amount of cleaning could reach between the glass.