MS Paint works for me on Windows 10, and I didn't do anything special, Here's what's in the configuration
windows_open_with.json file
Code:
"cmdline": "\"C:\\Windows\\System32\\mspaint.exe\" \"%1\""
You can download the 'old shiny' MS Paint via WinAero ==>>
Get Old Classic Paint for Windows 11 - should be okay for use in calibre's open with.
The 'new flaky' Paint is in Win11 Winapps folder, which is hidden inside the Program files folder… <sigh>
BR