Could you give me some advice on this piece of igcse descriptive writing? Thanks!

You've come to the right place. Randomly, my school to iGCSE English Lit and Lang in 2018, and I got a 9, with something like a top 50 grade in the country -- apparently I came 3rd!

'Patches of symmetrical snowflakes glee through the frosty air as the frigid cotton in the sky outs the toasted sun. Monstrous lines of trees camouflage under their silky white skin, their verdant strips of hair no longer to be found. Foggy mist from the breath suspended into the air as the pedestrian involved in amiable conversations, whilst their cozy cotton boots suffocate in the stocky snow. I glanced across the bleached and unpigmented streets behind a ginormous piece of window, as exuberant as the children on a brumal December.'

Okay, drop the unnecessary adjectives. King once called adjectives 'dandelions'; they look good until they cover your garden, then it's too late. If anything, stick to the basics, then layer it. Even though it's descriptive, let there be direction and a character journey, if you pull that off you'll win. All snowflakes are symmetrical, instead use something unusual to start. Love the rest of that line, just cut out a few adjectives to avoid making it decoration. Also, if they trees are monstrous, use this as a narrative, justify your use of language by following it up.

Why are they monstrous? Pick things out in concise detail to keep things both from moving on too fast and getting boring. Pick out people as though they are human, intimacy is important when building a character. Focus on a person in the crowd, or even better, the late friend who is making their way haphazardly towards you, revealing only at the end with a twist that they infact know you. Unpigmented is a useless word, completely extra.

Ingest this, there is too much to give advise on, and we all write differently. This mindset is how I did so well personally.