u could use an custom bash file that screenshots ur desktops, blurs it, and then sources it as ur lockscreen from a config file, in bash it could go:
#!/usr/bin/env bash
bg=~/.lockscreen.png
grim -o $bg
convert $bg -blur 0x8 $bg
hyprlock
rm $bg
havent tried it yet, but as long as ur sourcing the ~/.lockscreen.png on ur config file, or u launch ur locking program with an argument to use whatever u used as a background (and that way u can use mktmp instead of throwing it on ur home folder) it should work. Just try the commands b4 executing it since i wrote this from my bed on a saturday and my brain is half working.
i just used hyprlock as an example, since u said ur using hyprland, but u can use whatever ofc, I myself use swaylock.
thats beautiful