Since November 2017 if you change your search preferences to 100 results Google will ask you to confirm that you are not a robot.
This is to confirm that it hasn't been done by a rogue script or by automated crawling robots.
Here's how you change the number of results to a Google search.
1. Search for something on https://www.google.com
2. Click on the "Settings" word underneath the search box
4. Drag the block to 100 (or whichever number you wish) , for the number of results per page.
6. If you have chosen 100 you will get the captcha box, tick to say you are not a robot and click submit.
Your number of results per page has been changed.