Hi,
This may occur from multiple reasons, you can try doing the following :
Make sure the video is on Mute, as some browsers has it as a must for video muting for it to auto play.
Regenerate the CSS via Elementor > Tools > Regenerate CSS on your WordPress Dashboard.
To rule out the possibility of a plugin or theme conflict, please deactivate all your plugins besides Elementor and see if it helps. If it solves the issue, reactivate them one by one to find the culprit.
If it didn’t help, switch your theme (temporarily) to a default WordPress theme such as Twenty Twenty One and see if it makes any difference.`
