SUMMARY
Installing KWin Scripts by System Settings the Configure button is never visible.
The issue also occour by manual installation.

STEPS TO REPRODUCE
1. open systemsettings, "Window Management" > "KWin Scripts" section
2. click "Get New Scripts.." or "Install from File..." button
3. install some services (and optionally close and reopen systemsettings)

Manual installation:
1. download a .kwinscript file
2. install typing: kpackagetool5 -r something.kwinscript
3. open systemsettings and look at "Window Management" > "KWin Scripts" section

Example scripts with own configuration:
Sticky Window Snapping: https://store.kde.org/p/1112552
Tiling: https://store.kde.org/p/1112554

OBSERVED RESULT
The service was installed correctly, but the Configure button is never visible (for any services that expose it).

EXPECTED RESULT
The Configure button should be visible after service installation.

SOFTWARE/OS VERSIONS
Linux: Arch
KDE Plasma Version: 5.16.4
KDE Frameworks Version: 5.61.0
Qt Version: 5.13.0

Issue still present in this system too:
Linux: Kubuntu 19.04
KDE Plasma Version: 5.15.4
KDE Frameworks Version: 5.56.0
Qt Version: 5.12.2


ADDITIONAL INFORMATION
The cause of the issue is that the metadata.desktop file is never copied or symlinked into ~/.local/share/kservices5/ path.

Manually making a symlink seems to work perfectly:
mkdir -p ~/.local/share/kservices5
ln -s ~/.local/share/kwin/scripts/something/metadata.desktop ~/.local/share/kservices5/kwin-script-something.desktop

Further references:
https://techbase.kde.org/Development/Tutorials/Plasma4/PackageOverview
"Installation. By default, the metadata.desktop is copied into the the services directory..."