If I ever accidentally full screen a window, and it’s not in night mode, I am instantly blinded by a wall of mostly white empty background!
I frequently use macOS on a projector, it doesn't quite fill my wall floor to ceiling but it comes close. I don't use full screen often, but I do it occasionally as a focusing strategy, and it's fine.
You're shining a bright light on a wall, which you are looking at.
With a monitor you are shining a bright light at your face, while staring directly at the lightbulb!
If you're using a monitor in the dark the way you use a projector, you should turn the backlight down. If you're using it in a well lit room, the brighter backlight should have less of an effect.
It sounds to me you've never actually looked at a monitor display large swaths of white before, it's brighter than light hitting a wall for sure, even with the brightness down, extra so when the ambient lightning is dark too.
The fact that it's bright outside when the sun is up might help, but it's nowhere near enough to compensate!
It’s probably a me problem, but I’m going to open stuff and then leave it scattered around all day. It’s fine.
I don’t use more than a couple of virtual desktops either. Just one for current tasks and one for background apps.
My actual biggest pet peeve with this setup is the vast number of web sites that deliberately choose to limit their content to a tiny column centered horizontally in my browser, with 10cm of wasted whitespace on each side.