Tmux unable to have transparent+blur bg of alacritty

Not a req for support, just dropping a note that tmux does not get the alacritty transparent bg + blur. I have exactly same tmux.conf on another mach where it runs on xfce4 terminal w/ transparency (but no blur) and it gains that.

I tried a few things (mostly around setting "bg=defaul" here and there) but it did not work. My best guess is that the blur effect is the one that causes this.