No more video thumbnails from YT I guess? Also, why is the description in French? Also, if I put in an image that overrides the external link!

Invidious is very much like YouTube, and YouTube thumbnails haven’t worked on lemmy.ml since forever, and I don’t know why. The server is in France, which I think explains why the descriptions are in French.

Might it be possible, when creating a post, to be able to choose whether or not the post as it appears on the, I guess, feed (???) shows the link preview or an uploaded image if the OP includes both? Maybe there is already a way to do this . . . ?

You can add a "Thumbnail URL." I do sometimes, but it's lot of extra steps to generate an appropriate image and upload it to an image sharing site.