Appimages don't have all dependencies, just the variations in the target. FlATpaks do bring in the entire mini ecosystem...
Here is why I said what I said about the dependencies.Reference Link:How To Use AppImage in Linux [Complete Guide]Quote From The Article:
D. Things to remember while using AppImage in Linux
There are few additional things about AppImage that you should know.
1. Poorly packaged AppImages won’t run even with execute permission
The concept of AppImage is to have all the dependency inside the package itself. But what if the developer thought that he had packaged all the dependency but that didn’t really happen?
In such cases, you’ll see that even giving execute permission to the AppImage does nothing. You click on the AppImage and nothing happens.
You can check if there is such an error by opening a terminal and running the AppImage like you run a shell script. Here’s an example:
abhishek@itsfoss:~/Downloads$ ./compress-pdf-v0.1-x86_64\ \(1\).AppImage
/tmp/.mount_compreWhr2rq/check: line 3: xterm: command not found
Traceback (most recent call last):
File "compress-pdf_Qt.py", line 5, in <module>
from PyQt5 import QtCore, QtGui, QtWidgets
ModuleNotFoundError: No module named 'PyQt5'
As you can see, the AppImage I was trying to run had some packaging issue. If you encounter something like this, you should contact the developer and inform her/him about the issue.