Using krita 4.1.5

Smoothing the selection does not work. It usually just seems to grow the section and do no smoothing.

It would be nice if it worked like Photoshop and you you could enter an amount to smooth by.

Yes, that does seem like an oversight or a bug. It would be helpful if you could make a formal bug report here: https://bugs.kde.org/
The krita development team is small and busy but they do pay attention to formal bug reports.