how to stop safari 18.2.1 autoplay video on iphone

Note that if this is from websites, many are deliberately coded so that you can't stop the autoplay without third-party assistance. Look into StopTheMadness:

https://underpassapp.com/StopTheMadness/

which can stop many web-based videos from automatically playing, though not all.

Regards.

To stop Safari from autoplaying videos on an iPhone, you can:

• Hide distracting items
• Tap the menu icon at the bottom of the screen, then tap Hide Distracting Items. You can also select specific items to hide. 
• Turn off autoplay video previews
• Open Settings, then tap Accessibility, then Motion. Toggle off the switch next to Autoplay Video Previews. 
• Remove elements from a website
• Open Safari, go to the website, tap the Share button, then tap TapTap. If you don't see TapTap, go to Settings, then Shortcuts, then Advanced, and toggle on Allow Running Scripts. 

You can also block pop-up ads and windows in Safari by opening Safari, selecting Safari > Settings (or Preferences), and configuring the Websites tab.