Install yarn:

sudo eopkg it yarn
sudo eopkg install sqlcipher-devel
sudo eopkg it libsecret-devel
sudo eopkg install -c system.devel

Clone repository:

git clone https://github.com/vector-im/element-desktop.git

Edit package.json to target AppImage for Linux:

...
"linux": {
  "target": "appimage",
...

Install yarn dependencies and build it:

yarn install
yarn run fetch --importkey
yarn run fetch --cfgdir '' 1.7.25
yarn run build:native

Edit /element.io/config.json to change default server:

...
"default_server_name": "example-server.com"
...

Copy config.json to config folder:

cp config.json ~/.config/Element/config.json

Built executables are stored in the /dist directory.