Well, obviously I have just learned something new! I was always wondering, why my WordPress theme would support embedded Video formats, when in real life whenever I uploaded a video and selected video as my post format it just did not work.
O.K. so now while stumbling around in my backend looking for something completely different, I noticed a tab below my post editor, that I had never opened before. It´s a media tab and voilà there is an option that says: „Big White Stupid Apes Need To Insert Their YouTube URL Here When They Want To Use Video Post Types“ with a big pink neon sign!
Alright I get it.. so here is the difference… when you go to the blog overview, now you will see that I don´t have a normal featured image anymore. And I don´t need to include a video at the bottom of the post as well as a featured image at the top at all anymore. That is just double and freaked my out every time. Instead, you will now see a preview video right in the blog overview from now one. And on top of the post is the video. Just as I always wanted it to be. Nice one!
Editorial Afterthought: Well, Actually as nice as it looks in the backend, the video format is not supported on the frontend preview, so back again to the old display of things. So that messed up things pretty much. THX WordPress!