If you're using [uMatrix](https://github.com/gorhill/uMatrix), you'll not be able to automatically play a video served by Invidious on other websites without unblocking requests to Invidious instances.

So, to make it work, you'll need to allow `css`, `image`, `media`, `script`, `xhr`, `frame` for the instance form which you're trying to play the video.

Since there are more and more Invidious instances, you can use the tool called [Invimatrix](https://booteille.gitlab.io/invimatrix/) to automatically generate uMatrix rules for every known instances.