OP, based on how dated the flat looks, the LA block and how small the footprint is, it feels overpriced. Consider something like this to freshen up the kitchen for not a great deal of money: www.apartmenttherapy.com/400-dollar-green-white-kitchen-makeover-36772604
Some other thoughts:
Kitchen: Remove the frilly curtains; paint cabinets and replace handles (and perhaps tap) for something more design-led; replace the kitchen table and chairs with midcentury modern furniture (Amazon has Eames replicas for quite inexpensive prices)
Living Room: replace the light fitting; remove the curtains; consider repainting (although I suspect the colour will look a lot better without the curtains and with a better light fitting); swap the cushions for more stylish ones; declutter the shelves (remove the family photos that have been blurred and replace them with objects or books that would not need to be blurred)
Blue bedroom: Remove the pine dresser from the front of the shot; paint over the flowery wallpaper; dress the bed with large pillows so that the bedframe is not visible; remove the picture behind the bed; crisp white bedding with maybe a wool or fur throw for texture.
Other bedroom: Looks generally ok (although very small), would just remove the clutter around the side table
Bathroom: not much you can do without spending £££ but if you decide to re-decorate and re-take photos, maybe Aesop or other high-end hand soap and remove the random shampoos etc. from the picture
Balcony: As others have noted, the photos need to be consistent. The summer photo is gorgeous but expect you won't be able to recreate it for several months. If you will be re-taking the balcony photo, consider removing the table with lone plant pot on it and putting in some evergreen plants in the window boxes. Remove the winter photo from the listing.
Missing room: style this as an office if you can
Try to have one set of photos that clearly depict the same season -- these show a mix of summer and winter pictures, neither of which is the current season so makes me wonder just how old the photos are.
Generally, I think the flat needs to look a lot more aspirational for a young person to be interested, given Covid, financial crisis, Brexit and everything else that is going on. Brutalism is fashionable but your flat says ex-council rather than Barbican chic. If the flat projects the right lifestyle, it could still be attractive for a young buyer, despite all the changes to fundamentals.
Someone up-thread mentioned The Modern House as a source of inspiration -- that's a very good call as they feature several ex-LA flats that have been presented well.
See
www.themodernhouse.com/sales-list/rowley-way-x/
www.themodernhouse.com/sales-list/gilesmead/
In terms of price, could you afford to price it sub-£500k, even just below? It may result in the flat appearing on more searches.