Which AppImage should I install (.AppImage vs modern.AppImage)?

I'm installing the Ultimaker Cura 3D printer slicer program from here (https://github.com/Ultimaker/Cura/releases/tag/5.1.0) onto Linux Ubuntu 20.04. 1. What is the difference between Ultimaker-Cura-5.1.0-linux-modern.AppImage and Ultimaker-Cura-5.1.0-linux.AppImage? Which should I use? Why? How do they differ? I've [posted this on their forum too](https://community.ultimaker.com/topic/41214-which-appimage-should-i-install-appimage-vs-modernappimage/) . ### Update: important installation reminder to myself and others: After downloading the desired AppImage for your operating system, per the accepted answer below, be sure to make it executable as well! Then, you can double-click on it in a file browser to run it. Ex: how to install Cura on Linux Ubuntu 20.04:

# download it
wget https://github.com/Ultimaker/Cura/releases/download/5.3.0/UltiMaker-Cura-5.3.0-linux.AppImage 

# Make it executable
chmod +x UltiMaker-Cura-5.3.0-linux.AppImage

# Now run it. 
# Option 1: double-click the file in a GUI file manager
# Option 2: run it from the command-line:
./UltiMaker-Cura-5.3.0-linux.AppImage    # run in foreground
./UltiMaker-Cura-5.3.0-linux.AppImage &  # run in background

### Related: 1. My question: [How do I check or verify a pgp/gpg signature using a .asc PGP signature file?](https://unix.stackexchange.com/q/711976/114401)