I also have the issue, Windows 11, Version 24H2 (OS Build 26100.7462).
File version of Notepad.exe in "c:\windows\system32" is 10.0.26100.7309 and file modification date is 12/9/2025
File version of Notepad.exe in "C:\Program Files\WindowsApps\Microsoft.WindowsNotepad_11.2508.38.0_x64__8wekyb3d8bbwe\Notepad" is 11.2508.38.0 and file modification date is 11/8/2025
Executing "notepad.exe" in the run window throws the error "Mivrosoft.UI.Windowing.Core.dll was not found..."
Same error is thrown when notepad.exe is executed from the path "C:\Program Files\WindowsApps\Microsoft.WindowsNotepad_11.2508.38.0_x64__8wekyb3d8bbwe\Notepad"
Running notepad.exe directly from c:\windows\system32 works fine and the modern version opens.
Running reset did not help.
Running repair did not help.
Setting the default Path value in HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\App Paths\notepad.exe to c:\windows\system32\notepad.exe (which before was pointing to C:\Program Files\WindowsApps\Microsoft.WindowsNotepad_11.2508.38.0_x64__8wekyb3d8bbwe\Notepad) solved the issue for me.
I cannot resist to mention it again - How does Microsoft keep getting away with the plethora of bugs in their products? @Microsoft I suggest you use Copilot to get a list of broken things in your products to fix them.