>- No sudo, or at least no conflict between "Sudo is dangerous and can break your system" / "You need sudo to do routine things"

This is an unreasonable ask. No modern operating system will give you this. You have to escalate credentials on macOS and Windows as well. Typically Linux asks you LESS often than either macOS or Windows. This or I don't understand what you're asking here.

>- No CLI required to install software

Just use GNOME Software or Discover (KDE). They'll install anything on Flathub or in your distro's repositories. Use a different distro than Ubuntu though, since they are non-standard with using Snap instead of Flatpak.

>Lag-free pen experience

I have the same amount of lag in Windows as in Linux on my Surface Pro 9. What does need work is palm rejection, but you can disable the touchscreen while the pen is in use. Not the best.

>Good touch support

GNOME and GTK 3/4 apps are by far the best for this. Not quite as good as Windows though.

>Less fragile. I shouldn't have to worry about the PC booting up into a no-GUI terminal after I installed something, or edited a file. (See point 1; don't make me edit system files to do routine stuff like communicate with a USB device without sudo, if they can break the system)

?????? ?????? If you mess with system files on any system without knowing what you're doing you'll run into this problem with an OS.

>Let me open an application by double-clicking it

Double clicking what?

The executable file in your file manager? That works.

A desktop shortcut? Use a different DE than GNOME or install an extension that allows desktop shortcuts.