Some time ago I was a total Linux newbie too, no worries
The Linux OS is called Manjaro XFCE.
Amiberry, the Amiga emulator, is a Linux appliaction running on the Manjaro XFCE.
When you doubleclick AmiKit icon located on upper left corner of Manjaro desktop, Amiberry settings window is launched. When it appears, click Display and check some settings there - eg. the Auto Height as I mentioned before.
Just be advised that some settings cannot be changed while the emulation is running. So if you want to change something on the fly, press F12 (fn+F12) to show the Amiberry settings window and quit the emulation. Then launch Amiberry again, change some settings and start the emulation again.
Meanwhile I'll ask the author of Amiberry about the issue you are experiencing. Thank you for the screenshot! Btw. is the Manjaro Linux desktop cut off too? Or just AmiKit desktop?