I'm running Linux Mint 20 with no network connection. I'd like to run Arduino IDE 2.1.0 on it. I have acquired the AppImage. Upon launch the Window opens and shows a pulsating Arduino logo in the center. This goes on indefinitely. I have waited upward of 30 minutes, but the program never proceeds to another state.
I use 1.8.18 on mint and it runs just fine without a network connection. I have had no luck with installing the Applimage format. I use sudo apt install ..., it works every time. I just installed Mint 2.1 and installed 1.8.19 and it has connection problems, works for a while then drops out, the message still appears on the scope. The same machine booted with mint 18.3 works just fine with 1.8.18.
On the first run after a fresh installation, Arduino IDE downloads some additional essential components from the Internet and installs them. If it can't install those components then the startup fails. So the computer must have access to the Internet on the first startup.
After that first run, an Internet connection is not required. However, there are some supplemental features such as "Library Manager" that have an inherent dependency on the Internet. Those features will not be usable while your computer is offline. But the essential functionality of editing, compiling, and uploading sketches will be available even without an Internet connection.