The wallpaper is just a cropped image from the scans of the games manual found here, note these are spoilers!, Tunic is an absolutely lovely game I have been playing on my Switch and I highly recommend it to people who really enjoy the difficulty of older Nintendo games but want a more polished experience. The way the game integrates the "manual" is really intriguing
For a while I was experimenting with different plasma themes but I landed back on the good old reliable gruvbox dark theme.
Edit: my apologies for not perfectly aligning two of the images in Gimp, I forgot to press the button that aligns them horizontally and not just vertically :p
It definitely is rather reminiscent of older Windows versions with the seperate application launchers, fully expanded task bar entries that show the name of an app that are ungrouped (until necessary). And the widgets are very reminiscent of Rainmeter.
But I also bring some things from macOS that I enjoyed such as the global menu on the top (sadly Firefox flatpak does not support), virtual desktops with the pager widget on the bottom, and I use Krunner a lot (plasma's equivalent to macOS "Spotlight")
I hope your switch to Linux goes well if / when you switch!