The Helm Chart for APM is really meant for 7.x, in 8.x there were significant changes that require additional configuration than what the helm chart offers. These instructions are probably better. The APM server that the Helm Chart offers is considered "legacy". If you want a slightly better out of the box experience, I'd recommend looking at the Elastic Fleet & Agent setup, which offers the APM server as an integration, and is "simpler" to get setup.