I’d find that shocking too, especially the access to social media like TikTok.
In contrast, my DD is 10 and I’d say only a few children in her class have phones (mainly for contact with separated parents). Her school has signed up to the Smartphone Free Childhood pledge (mentioned by previous posters) and a lot of the parents are supportive. I can see that with a different ‘school culture’, it’s more difficult to enforce restrictions when no one else does.
The school hosted a talk from the group which was quite eye-opening - the police liaison officer there said that issues they had previously seen at secondary school (grooming, inappropriate material being shared) are now happening at primary schools.
Having said all that, my DD is allowed to play Roblox, with parental controls, and I know the social aspect is important. However, she only plays on the family laptop when one of us is around. Likewise she can watch YouTube but again only on the family laptop or my iPad, when we’re around. She doesn’t have her own iPad or tablet as I think she’s too young, though some of her friends have their own. We were quite strict about screen time at age 8, but now we’re a bit more relaxed as she can regulate herself a bit. However, I do make the effort to keep her busy, especially at weekends, to reduce the time she can go on the laptop.
I also agreed with the comments that @Ecrire made about how your DD sounds overlooked in a busy household, including not being able to have swimming lessons because of her younger siblings schedule (if I’m reading your posts correctly), but I see that you have responded in a later post.