Hi - well, as long as you’re using “menu bar” to refer to the panel with the application menu, task buttons and system tray, then yours isn’t a totally unheard-of concern - hopefully you can take some solace in that! Show/hide main panel with a hotkey
And there is a pretty long-standing submitted feature request on that topic: 158556 – "Manual show" option for hidden panel controlled only by pushing a button on a widget somewhere else
With the extent of discussion that’s happened over the years, it looks like something that just needs a person with the time, interest and ability to dive in and figure out how to implement it 
If that might be you or someone you know, the KDE Community Wiki has a great resource for getting started working on and contributing code: Get Involved/development - KDE Community Wiki
I’m personally an “always visible” panel user, so I’d have to defer to others for any hacky ideas to work around that situation - although it might be worthwhile playing around with different pointer speed or acceleration settings, if it’s been a while since you’ve done that?