In my case, the default scale is too small, but the zoom screen support helps me too
About the max zoom level, it is still a bit small for my screen (especially, for side panes).
The max zoom level seems to be 125%, although I couldn't know it as we cannot (?) test
BTW, shortcut keys for Issue (to archive it etc,), "Zoom +" etc. seem not to work on Linux, although they are not big problems to me for now.