FS-UAE and Retropi (PC) questions

[gagagu]

Hi all,
i am using Retropie on an old Laptop based on Ubuntu 18 for playing old Amiga games. I've installed fs-uae with the ipf Plugin successfully on it. I've many Aminga games in ipf Format all in separat zip files. I've extraced one zip and copied the file to the Amiga roms folder and loaded it with fs-uae. It runs fine.
But i have only two issues to solve to make everytjing perfect and i Need you help to solve it. I#ve aready used Google and this Forum search but everyone seems to use the fs-uae launcher but i'm using it in retropi so the solution are all not working for me.

1. Fullscreen
   The Amiga window is shown in Retropi but it's not Fullscreen (Retropi is shown in Fullscreen). I hit F12 to bring up the menu and click to the fullscreen Symbol. The window is now shown in Fullscreen but than the Ubuntu Navigation bar is shown. What i have to do to show the Amiga window in fullscreen?

2. ipf file with several disks
   As i wrote before i have some games where some disk Images of one game are stored in one zip file
   Game XX (Disk A).ipf
   Game XX (Disk B).ipf
   Game XX (Disk C).ipf

or
Game XX (Disk 01).ipf
Game XX (Disk 02).ipf
Game XX (Disk 03).ipf

I've extracted the zip file and copied the three files to the Roma/Amiga folder. The first ist that all three files are shown in Retropi as game which isn't really beautiful. When i will load the first disk it will load but i do not know how to switch to the second (or third) disk. The F12 Menu is on the first view not really helpful.

What i have to do with such games with several disk files? Do i have to copy the zip file instead of the single extraced files to the Rom folder?

btw: I'm new to ubuntu

Thanks Forward for your help!!