i don't know why but the exit and all keys of pamac manager are missing, is that some type of glitch?
Reapply the GTK theming in KDE settings
Yes; this seems to happen if you move the window title bar buttons (close, minimise, maximise) to the left-hand side. Either leave them on the right, or try a different window theme.
whenever i change any theme pamac manager is least affected but at least the buttons appeared
I assume you are using KDE. Pamac is one of the GTK apps that just never seems to integrate well into a Qt environment. If you are on KDE you can always give Octopi a try (or Discover for that matter).
Discover is actually a great app for simply browsing for software, but I would never recommend it for doing system upgrades. Discover is prone to crashes, so don't rely on it for installing. If you are simply using any of the GUI intallers as a software center to browse for new apps then any of them will do.
However, for performing system upgrades I would not reccomend using any of the GUI package managers. Especially for large system upgrades, I would always recommend using Pacman.
It's not that difficult, simply use:
sudo pacman -Syu
Actually pamac-all works great. I ran across this issue under EOS and once I switched themes all was good again. So try that first would be my suggestion.