As per Google support, there is a toggle that can be used to enable/disable Autoplay feature on YouTube.
However, I cannot fine this toggle in this video:
Could someone give a hint?
Stop looking for the toggle, instead, just don't open the video if you don't want to play immediately.
The lack of the toggle might be b/c the referred video isn't from a regular YouTube account but from the MIT Courseware account, one of the pioneers universities on making university regular lectures and other related course material being open (available for free) on the Internet. Not much time for now for giving details, but the toggle is missing on other videos of the same account and might be missing on videos from other similar accounts, I mean education institutions that have made some sort of partnership with YouTube.