This is a community-maintained Flatpak distribution of Element Desktop, formerly called Riot.
Element Desktop's instructions to use user-specified configuration settings do not apply. Instead, config.json must be created at ~/.var/app/im.riot.Riot/config/$NAME/config.json, where $NAME is typically Element. The contents of the file are otherwise the same.
Overriding enviroment variables such as all_proxy, http_proxy, https_proxy can toggle proxy for Element Desktop. For example:
# enable proxy
flatpak override --env=all_proxy=http://127.0.0.1:7890 im.riot.Riot
# disable proxy overriding and use proxy settings from system (if current-shell env have related variables)
flatpak override --unset-env=all_proxy im.riot.Riot
# disable all proxy settings (Flatpak shell will inherit env from host shell sometimes)
flatpak override --env=all_proxy="" --env=http_proxy="" --env=https_proxy="" im.riot.Riot
