Menial routine work for juniors has been eliminated or automated to the margins, that much is true. No office-boys and far fewer supermarket cashiers. For those with people skills, there's plenty of café work, but that's about it.
On the flip side though, the educational/academic landscape for the upper quartile of young adults is hugely more competitive. Nobody is making it to a Russell Group uni on cruise control, and getting top grades AND having a part time job AND hobbies and a social life isn't easy.
Then you have menial work that's actually fairly skilled. Social care, childcare and so on. That's not something a student is going to do for a couple of years on the way to something better.
And a shift, for various reasons, to the contracted-out agency model for cleaning. Mostly done by immigrants, but they work harder than most semi-retired Brits would be willing to. Even if they're less flexible than the old boy who'd fix a bad door or window as well as sweeping the floor, and have none of his loyalty.
UberEats on the other hand is taking the mick. A lot of their workers are undocumented, the self-employed contractor status allows the operator to avoid the normally stringent penalties for immigration law breaches. I don't know if they lobbied for the law to be that way, but it's a massive loophole. So this is illegal work and maybe shouldn't be conflated with legit immigration. How much it's a problem I'm not sure.. the actual numbers are quite small, but like the loudspeakers on the bus thing, it's a very visible breach of the norms and rules, so there's an argument that it's bad for society on that basis. And like I say, the operator is blatantly exploiting it, they can't be blind to what's going on. I'm pretty liberal on immigration, miss the positive contribution the former Eastern Bloc countries made prior to Brexit, but the whole food delivery sector is overdue a clean out.