In Admin, when there is a pager, there could have a dropdown that allows to select the number of elements per page that you want to display.
It would contain the current PageSize (often 10, but can be a setting like site.PageSize) and other default sizes like 20,50,100.
It would be bound to the PageSize option of the pager.
Pager in O1 admin:

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Pager in O1 admin:
