$APPDIR environment variable not usable in AppRun shell script?

[OWL4C]

Hello, i've been trying to build an AppImage with AppImageTool, and got as far as having the AppDir up to Code and creating the appimage binary. However, when running exec '$APPDIR/usr/bin/<exe>, i get the error that /usr/bin/exe is not found, and checking with echo also confirms that $APPDIR is empty.
I can upload the script and link it here, including the entire fork/project i am trying to package. (The AppRun is contained in the Buildscript at line 34ff)
https://github.com/OWL4C/Blender-Launcher-V2/blob/main/AppImageBuild.sh
https://github.com/OWL4C/Blender-Launcher-V2

[probonopd]

You cannot rely on $APPDIR being set. Why are you not using something like HERE="$(dirname "$(readlink -f "${0}")")" in your AppRun?

[OWL4C]

Because i have no idea what i am doing.
I was just using https://docs.appimage.org/packaging-guide/manual.html and https://github.com/AppImage/AppImageSpec/blob/master/draft.md#appdir none of which really went into any detail on the AppRun.
Using HERE="$(dirname "$(readlink -f "${0}")")" just gives me the path to the working directory, even though the error clearly lists the tmp/.mount so i am really confused.
I am also guessing it would be easier (for this simple case) to use a symlink as AppRun like linuxdeploy does.

EDIT: where would be the relevant docs for this? I haven't found that many good docs / tutorials for this, probably since the usual way wouldn't be low level appimagetool?

[probonopd]

Correct, appimagetool is mainly meant as a low level tool that converts a working AppDir into an AppImage. Your question is about how to create a working AppDir. There is no simple short answer that fits all scenarios. You need to make your application relocatable in the filesystem and bundle the necessary libraries in the AppDir.

There are various tools to assist with this task:

https://github.com/AppImageCommunity/awesome-appimage?tab=readme-ov-file#appimage-developer-tools