Hi Silvio, first of all, thank you for your purchase and support!
Regarding the window moving lag, the following note is mentioned on my website in FAQ > Limitations. Is it what you had in mind?
"Linux windows make "ghosts" effects when moving them. You can always prevent that by enabling "display compositing" in "Compositor" tab of "Windows Manager Tweaks" settings, but be advised that it also decreases the Amiga emulation speed considerably.
Regarding .lha or .adf files - this heavily depends on your overall AmigaOS knowledge.
I created some tutorial videos which might help you understand some specific areas. For example how to unpack an LHA archive: https://www.youtube.com/watch?v=qY5kiVzLBC8&list=PLxEnP5UUSCcREBN5C0aCC-zZ5H_gK4FTV
ADF files are floppy disk images usually including a game or demo. They can be "inserted" to Amiberry emulator and booted (even without AmiKit!). If you want to launch them from AmiKit, they can be installed using WHDLoad installer. Try to google some basics first. Or join us on Discord where the community can help you live. Just click the Discord link on your personal download page.