The tooltip issue can be fixed by increasing the delay for them to appear (or even deactivate them, but they are still useful).
Engine/Config/ConsoleVariables.ini (To make it permanent)
Slate.EnableTooltips=1
Slate.TooltipSummonDelay=1Console:
Slate.EnableTooltips 1
Slate.TooltipSummonDelay 1
As for the graphical glitches when moving windows on top of the editor, it only happens on Plasma. So if you want to use Unreal without these glitches, you will have to use GNOME or Cinnamon or I think another GTK-based desktop environment would work.
On X11, there are still some bugs, where the mousse behave weirdly. This can be fixed by adding the -nohighdpi argument when starting the Editor.
For the editor freeze, this is probably due to my GPU being too old for the Vulkan renderer that is used on Linux (I does not have this issue on Windows, but DirectX does not needs that much VRAM compared to Vulkan). It is quite annoying, but now that I fixed almost every issue, the engine is still pretty much usable on my laptop with linux.