Hi! I'm the developer for nvui (didn't realize this post was made, never used this forum before). The animation durations and a few other things about them are customizable if you look into :h nvui-multigrid and :h nvui-cursor.
As for the GIFs, I didn't expect them to come out badly (don't know if it was compression, but they didn't look that bad when I uploaded them. I'll look into making a "media" branch.