How to show a YouTube fullscreen player when I click a youtube url?

All you need to do is paste the URL to the video into your post, Blot should do the rest. If this isn't working for you, please send us a link to the post and we'll investigate further

I don't want to embed (pagespeed optimization), I want to click a button/link/picture and open a fullscreen lightbox youtube player.

Is this possible?

This isn't a built-in feature of Blot but it's possible to achieve yourself with some custom JavaScript on your template

Otherwise I'd suggest just a text link to Youtube