I fear the situation is much more dire. In fact, I'm honestly not certain .bat|.cmd files
ever worked with the Open With feature before Windows 10. Something with Windows 10 seems to have changed, but all examples of using QProcess::startDetached() to run batch files on Windows that I've run into seem to suggest that it's "cmd.exe" that needs to be launched. And that the batch file needs to be one of the arguments to cmd.
Something like:
Code:
return QProcess::startDetached("cmd.exe", {"/k", "C:\Path\to\mybatchfile.bat"}, "C:\Working\Dir");
If true... then the Open With feature of Sigil is going to need a bit of an overhaul to support launching exes AND bat|cmd files on all supported versions of Windows.