The method I use to install FS-UAE on my Pi4 uses the Raspberry PI OS as it's base, but any other debian based OS will work the same.
Simply open a terminal and type the following commands:
echo 'deb
http://download.opensuse.org/reposit...ble/Debian_11/ /' | sudo tee /etc/apt/sources.list.d/home:FrodeSolheim:stable.list
curl -fsSL
https://download.opensuse.org/reposi...11/Release.key | gpg --dearmor | sudo tee
/etc/apt/trusted.gpg.d/home_FrodeSolheim_stable.gpg > /dev/null
sudo apt update
sudo apt install fs-uae fs-uae-launcher fs-uae-arcade
Hope this helps