i3lock with screenshot (oli-like blur)

lock.sh

#!/bin/bash
FILENAME=/tmp/.lock-bg.$USER.png

# cleanup previous run (if any is remaining)
rm $FILENAME

# wait for rofi to close (optional - uncomment if you don't wanna see a leftover of rofi menu)
#sleep 1

# take screenshot and blur it in memory, and dump only blurred version to disk
scrot -z - | magick convert png:- -blur 3x2 -paint 3 "png:$FILENAME"

# lock screen as a bg job
i3lock --image $FILENAME &

# wait for i3lock to read the screenshot and immideately delete it from disk
sleep 1
rm $FILENAME

# wait for i3lock to finish
wait

This is how it looks. Modify arguments of blur and paint in magick convert to tweak the effect.