Depending on the file extension, it may work (if you have custom extensions), but if you have "basic extensions" like .txt, jpg it's better to not set your app as default program for all files with this type. Unless you created e.g. a new image viewer (to show / edit png files) to replace the windows app and you only want to use your app to open this :)
@Kuczmil in addtion to @SGaist suggestion of making your class/library "GUI-less", i.e. having no widgets at all, you may want to check the xvfb virtual framebuffer X server for X Version 11. From documentation:
Xvfb is an X server that can run on machines with no display hardware and no physical input devices. It emulates a dumb framebuffer using virtual memory.
Earlier Qt for Embedded version provided a virtual framebuffer which allow for simulating different displays when no actual hardware was available...
Whether you use OpenGL and eglfs or not does not matter here at all - you are using QtWidgets (which are drawn using CPU, not GPU) and you are displaying a GIF animation (which is rendered by CPU, not GPU). My guess is that RPi Zero is just too weak to handle this task.
Maybe try displaying the movie in some other format, which might be hardware-accelerated on Raspberry (not sure if Zero model has acceleration for any format).
libQt5Widget.so.5 not found
libQt5Network.so.5 not found
libQt5Gui.so.5 not found
libQt5Gui.so.5 not found and so on....
These errors show that Qt libraries where not installed in the device (target) where you want to run your app.
Since you built the app in another device (host) and then you said you replaced those files until another different error appeared, right?
I replaced the file libstdc++.so.6.
when I want to execute this file on terminal, I have this error:
“GLIBC_2.18 not found ”
Well, it seems that although your devices (host and target) could be the same hardware version, they don't have exactly the same OS version (and supporting libraries)