This isn't going to be popular, but I think blaming the schools is a red herring. I think it's because kids in the UK have a lot less independence than kids in many other countries, and have become frustrated. They start school much younger than Europeans, but they are treated like babies a lot longer.
From what I have seen of families in the UK at the moment, as well as a lot of the a lot of the threads on here, parents in Britain continue to expect to directly supervise their children to a much older age than the average European.
Kids in the UK are expected to start learning to read when they are still seen as far too young to walk to school or play out with friends. Where we are (central Europe) we also have overcrowded, boring schools with too much assessment and emphasis on one type of student. We also have problems with screens, bullying and the rest of it.
BUT our children don't start school until they are 6 years old. They don't start learning to read and write until halfway through the 1st grade. From age 7 they take themselves to and from school. At age 10 they all do a cycling proficiency test (free, organised by the school, during school hours) and from then, they take themselves to sports and activities hang out with their friends etc - like 1970s UK.
We also have plenty of traffic and all the other issues, but we teach our children to manage the risks, and then allow them to manage a lot more of their own lives. We still parent our children, know where they are, and care very much about the risks. But for us, we show our caring by allowing our children to develop the skills and the confidence to manage their own movement.
All of my children could safely cross a road and go to the shop by themselves long before they could read fluently.
We live in an area which is visited by a lot of young backpackers during the summer. It is very noticeable that the European young people know how to find their way around, clean up after themselves etc, whereas a lot of the British ones, at the same age, seem very immature and unsure about how to approach strangers or find their way around, oblivious to picking up their own rubbish etc.
I don't mean to cause offence, but I really do think this is a part of the problem. I grew up in the UK during the 1980s/early 90s and it seems to me that the "normal" amount of freedom young people are allowed there has decreased drastically.