How can I achieve conditional page breaks in SSRS 2016
Another workaround, which seems to work quite nicely - place a parent group of the group you want to selectively break on, then in Group Properties for that, group on a derived expression of either the group field, or a fixed value. And then tick the box for that grouping as per your screenshot.

e.g. Assuming a parameter called "BreakPages", and a grouping on a field called "MyGroupField", you group on:

=iif(Parameters!BreakPages.Value="Y", Fields!MyGroupField.Value, "None")


You don't need to display any fields in this special group, it'll simply use the page break setting as per your requirements..