When closing the inventory, container, or creative inventory; the mod causes the screen to flash black for a a quick quarter of a second. I tweaked every setting and no change was made. I narrowed this down from 200+ mods and I couldn't tell you if another mod combined with Blur+ causes the issue.

I’m experiencing the same issue. It seems like Jade’s UI is conflicting with the Blur animation. I only get the black screen during the fade-out animation when Jade is enabled and I hover over a block. Disabling or removing Jade resolves the problem.

Here's a workaround for now while it's still broken: turn the Fade Out Time slider in the Animations option menu down to zero. This disables the animation that plays when you exit screens, which is what is causing the problem.

I didn't notice the black screen on Windows, but it was definitely there on macos with automodpack on 1.21.1. Removing the fade as mentioned above totally fixed the problem as a workaround.