This is a highly configurable SDDM login system.
Free and open source software of course, MIT licensed.
It ships with 5 complete visual setups right out of the box (4 static images, like the one you saw, and 1 looping video), and you can tweak literally everything through a single theme.conf file.
You can swap the background image or video, adjust blur intensity, change fonts and sizing, shift the form layout (center/left & right), change animation easing curves, and customize every single color hex across the text fields, buttons, and hover states.
So, I've been running Linux exclusively for many, many years at this point.
Over time, my setup has evolved into a highly tuned terminal centric & keyboard driven machine, and I've decided to start open sourcing parts of it to give back to the community.
There are many tools I've built for my personal
SOCIAL SHARE CARD GENERATOR