"The collapse of international mobility and therefore immmigration is a key factor behind wages growth acceleration in advanced economies."
I don't see any support for that assertion anywhere though.
If you're missing 2 million people who would happily take low wage jobs, and there are as many of those jobs to do, the price paid for that work has to go up.
That said, I suspect that the great resignation has a whole lot of impact as well. Again, reduced supply causing an increased price. (The ones who walk away from bad jobs into good ones not being as impactful as the ones who took early retirement post-COVID, accelerating a worrisome demographic trend of having lots of old people and few working age people.)
Another plausible explanation is that the boomers are aging out of the workforce, and the following generations are smaller.
Seriously, that was the entire point of what I said there. That there is another factor which I suspect is even bigger.