On Linux, in order to reduce the clutter in the user's home directory, Avidemux could use the XDG Base Directory specification (https://wiki.archlinux.org/title/XDG_Base_Directory) for its configuration directory (.avidemux6).
For backwards compatibility, the configuration would be read initially from the current location (~/.avidemux6). If not found, it would be read from $XDG_CONFIG_HOME/avidemux/avidemux6, with $XDG_CONFIG_HOME defaulting to $HOME/.config if not set.
$XDG_CONFIG_HOME is the user-equivalent of /etc. Meanwhile, putting configuration in the home directory is analogous to putting system-wide configuration directly in /
This was already mentioned here (https://avidemux.org/smif/index.php/topic,17111.msg76778.html).
Those are missing in every Debian/Ubuntu based distros by default, which combined give the majority of desktop linuxes.
The specifications (https://specifications.freedesktop.org/basedir-spec/basedir-spec-latest.html) do state that it is totally fine to leave $XDG_CONFIG_HOME unset, in which case the default path (~/.config) is used. It is rather the recommendation to split configuration and user-specific data (e.g. custom scripts) which feels like an unnecessary complication in case of Avidemux.
By all means, there is no ideology behind this being not implemented yet. Just complacency and a sky-high pile of important stuff needing a fix.