Maybe it would be nice to add new action "Minimize All Windows" under System Settings -> Desktop Behavior -> Screen Edges which works very similar to "Show Desktop" action but other windows stay hidden/minimized after opening Application Menu or just one specific window. Basically identical functionality to "Minimize Windows" widget but can be activated by moving mouse cursor next to corner (screen edge).
An alternative option would be to adjust "Show Desktop" option.
Makes sense to me given that a lot of people prefer the "Minimize All" functionality instead of "Show Desktop".
However Phab tasks are best suited for tracking large-scale projects that require close coordination with multiple people and potentially multiple patches in different repos. That doesn't really seem to apply here. So can you re-file this as a bug report? Thanks!
Done, created this bug report: https://bugs.kde.org/show_bug.cgi?id=407117
Thanks a lot for clarifying details.