I full screen a Gnome-Terminal (but any terminal will work) and set the transparency. For me I just type F11 and it goes into full screen.
I find a good background video on YouTube that is okay with copyright and loop that in full screen as well.
I find a good sound effect or music YouTube video, again with no copyright restrictions, and loop that as well.
It is a little hard to manage them. But I have gotten used to managing everything with Alt-Tab (Command-Tab for me) so I can switch between them fast enough when needed.
I have been really loving PopOS Super key window zooming so I can get
a quick look at everything in real-time even while still displaying.
This is particularly important when streaming with hotkeys for important
things like hiding your screen to do scary stuff. You can tap Super
just to glance at OBS to make sure the preview is what you expect before
doxing yourself.