For example, this page shows:

How China’s population has changed since 1950 with reference to the start and end of the one child policy.

This page discusses: 1961: Introduction of the oral contraceptive pill in Australia

Yes, you're right. Immigration muddies the statistical waters when looking at population growth. We have - did haved before COVID, that is - a fairly high immigration rate so this page shows a chart of birth rate in Australia since 1935:

birth rate

After the post-WWII baby boom there is a significant drop to below the 1935 rate from around the time that contraception became available.

Note: in my post-grad management degree I studied a statistics module for one semester. I like stats but it's not my main area of interest, though I confess to being a spreadsheet nerd.