[kde] Icons vanishing in KDE Plasma panel + replacement app for Caffeine

Hi guys,
I'm still quite fresh in Linux and I've used KDE Plasma (current version KDE 5.68.0 / Plasma 5.18.5) for only around two years mostly in Kubuntu (20.04. Kernel: x86_64 Linux 5.6.17-050617-generic). Before I used Gnome in Ubuntu.

My two questions are:

1. I've noticed a bug in KDE Plasma desktop, that when you create a "panel" (e.g. in bottom of the screen) and you add apps in that panel (icons), that some of these app icons vanish always after reboot. The apps do still function when you click their icon, but the icon itself has just vanished. Icons sometimes reappear after reboot. This vanishing seems to be arbitrary. Are there any solutions for this?

2. I grew quite fond of Caffeine app in Ubuntu's Gnome DE witch enabled me to leave the laptop screen on with a push of a button. However, Caffeine does not work in KDE Plasma. What kind of other ways are there to leave the screen on in KDE Plasma with a very simple way, e.g. keyboard shortcut, push of a button etc.? I couldn't find any naive native KDE Plasma settings which would enable such functionality.

Thanks a lot!!