They also have the same issue with the Responsive Lightbox plugin and WordPress 5.6 upgrade.
https://ww.wp.xz.cn/support/topic/break-the-site-since-wp-5-6/
I also have that previously activated “Responsive Lightbox & Gallery”.
Responsive Lightbox & Gallery allows users to create galleries and view larger versions of images, galleries, and videos in a lightbox (overlay) effect optimized for mobile devices.
I will try to reactivate all plugins except for that one. Let see what will happen. I can recall why I installed that in the first place. I guess it is a crucial plugin to have but if that caused the black screen, I guess I will have it deactivated for now.
We have the same case. There’s this black screen that pops up above your page with an x (close button) that does not work. What I did was deactivated all plugins and now, I am re-activating it one by one to see which plugin causes this.
It started when I updated to WordPress 5.6
