All desktop icons have disappeared and Task Manager cannot be launched.

This has also happened to me. Once when upgrading to 25H2 from 23H2, and again just now after upgrading from 24H2 to 25H2. I'm on build 26200.6899. Everything seemed fine until I switched my PC on. The only way I could get the desktop back before was to do a repair install via Windows Update, and I'm having to do so again now. Clearly, though, this is NOT a permanent solution as it has happened again. Something is seriously wrong with 25H2. Signing in and out did nothing, System Restore couldn't initiate due to a catastrophic error, and the mouse and keyboard wouldn't work if I tried to use Advanced Startup. 

The solution cannot be found by anything the user attempts, except for doing a repair install. Why should we keep having to do this!? Microsoft are the ONLY one that can permanently fix this.

Hi, I'm having the same issue, ever find a fix?

Even though the desktop is gone, you might be able to do this if you can access a command prompt.

Press Ctrl + Alt + Delete. This security screen often works even when the desktop is broken.

Select "Task Manager" from the menu. If it actually opens, great! If not, proceed to step 3.

If Task Manager doesn't open from there, look for an option called "Sign out". Signing out and back in will restart all your user processes, including Explorer, which often fixes the issue temporarily.